May one drink tea or coffee, water, and other beverages after Kiddush/Kadesh and during Maggid?
Wine and Alcoholic beverages: If one desires to drink a number of cups [of wine and alcoholic beverages], whether immediately after Kiddush or in middle of the Haggadah, prior to beginning the blessing of Asher Goaleinu, then from the letter of the law it is permitted for him to do so [if it does not require another blessing of Hagafen as will be explained]. Nevertheless, it is proper to beware not to do drink wine, nor any other alcoholic beverage, prior to finishing Maggid and drinking the second cup of wine [and so is the custom]. Nonetheless, in a case of great need [such as there are no other beverages available and one is very thirsty, or one needs to say Havdalah, or he desires to draw an appetite to eat the Matzah] it is permitted to drink even alcoholic beverages. However, the above [letter of the law, and time of need, allowance] only applies if one does not need to say a new blessing of Borei Peri Hagafen upon drinking more wine, such as if upon reciting the blessing over Kiddush he intended to drink more wine afterwards during the meal or prior to the meal. However, if he did not intend to drink more wine [at the time of the blessing] and then changed his mind and decided to drink more wine (before the meal) then since he is required to recite a new blessing of Borei Peri Hagafen, just as he recites upon drinking any of the four cups according to the Ashkenazi custom, [then it is forbidden to drink it, as] it appears like one is adding to the number of [four] cups [which the Sages required].
Chamer Medina-Tea, coffee, pure juice: All beverages that are defined as “Chamer Medina,” which are all beverages that are significant enough in ones country for one to be able to fulfill his obligation of Kiddush with [i.e. tea, coffee, pure juice] are prohibited from being consumed between the first and second cup of wine, if he needs to recite a separate blessing [of Shehakol] on the beverage [such as he did not have in mind to drink them upon reciting the blessing of Kiddush, and they were not on the table at the time]. (This prohibition to recite a new blessing on Chamer Medina beverages applies even if one will be drinking wine to fulfill his obligation of the four cups, and not the Chamer Medina beverages.) [If, however, a new blessing is not required to be said over them, such as if one had them in mind upon reciting Kiddush, or the beverages were already on the table, then one may drink them without restriction. Thus, we find that some are accustomed to drink coffee before Maggid, if they feel they need it.]
All other beverages: [After Kadesh, until the blessing of Goal Yisrael in Maggid] it is permitted for one to drink all beverages other than the above mentioned [i.e. one may drink non-alcoholic and non-Chamer Medina beverages], without restriction. This applies even if one is required to say another blessing prior to drinking the beverage [i.e. such as he did not have them in mind while saying the blessing of Hagafen, and they were not on the table at the time].
Saying an after blessing after a drink: In all cases that one drank a Revius of a beverage after Kadesh [i.e. water, tea, coffee, juice], nevertheless, one does not recite an after blessing of Borei Nefashos, as it is included in the after blessing of Al Hagafen that will be recited after the fourth cup. This applies even if one was required to recite a before blessing of Shehakol over the beverage, as explained above. This law applies anytime one drinks a beverage from after Kadesh until the end of the Seder.
After Kadesh, prior to the end of Maggid, one is to avoid drinking any wine or alcoholic beverage, even if a new blessing is not required to be said. However, one may drink any other beverage without restriction with exception to coffee, tea, and pure juice, in the event that a new blessing must be recited upon drinking it. If these beverages were already included in the blessing of Hagafen said earlier, then it is permitted to drink even these beverages without restriction.
 See Admur 473:11-13; Kaf Hachaim 473:35-41; Piskeiy Teshuvos 473:10; Nitei Gavriel 80:1-5
 Admur 473:11
 Admur 473:11; Michaber 473:3; Mishneh Pesachim 117b; Tosafus Pesachim 103b; Razah [Baal Hamaor] Pesachim 24a; Peri Chadash 473:3; Chok Yaakov 473:5; Aruch Hashulchan 473:6; See Nitei Gavriel 80:5 footnotes 11-12
Other opinions: Some Poskim rule it is forbidden to stop in middle of the Haggadah for a drink, once the second cup is poured. [M”B 473:4; Biur Halacha “Hareshus”; Shaar Hatziyon 473:9 Levush 473; Biur Gr”a; Ramban in Milchamos; Ran; Maharam Chalvah Pesachim 117; See Kaf Hachaim 473:21]
 Admur ibid; Chok Yaakov 473:11
 Darkei Moshe 473:5; M”B 473:14; Kaf Hachaim 473:38
 Admur ibid; Michaber ibid; Kol Bo 50; Chok Yaakov 473:11; Kaf Hachaim 473:37
The reason: In order so he does not get drunk and end up not reading the Haggadah. [Admur ibid]
 Kaf Hachaim 473:39; See Admur 473:7 regarding Havdalah
 Admur ibid
 Admur 473:12 writes that if one specifically intended to drink more wine a new blessing is not required, however in 473:7 in parentheses he writes that so long as one did not intend to not drink more wine he is not required to repeat the blessing [even if he died not intend to drink more wine]. Vetzaruch Iyun!
The law if the wine was on the table: In general, the Poskim rule that having wine on the table is equivalent to having in mind to drink it, and hence a new blessing is not required to be recited. [See Admur Seder 1:21; Luach 5:11; 174:4] Thus, likewise here, if the wine was on the table one may drink it without a blessing even if he did not have it explicitly in mind, so long as he did not explicitly intend to exclude it. [M”B 473:3 in brackets; 1st explanation in Shaar Hatziyon 473:18; Possible intent of Admur 473:7 in parentheses; Nitei Gavriel 80:1] However, from the omission of Admur in 473:12 of any discussion of the law if the wine was on the table at the time of Kiddush [as is common by every Pesach Seder probably since its inception] it can be assumed that it makes no difference, and so long as one did not explicitly have in mind to drink it, a new blessing must be recited, as it is not customary to drink wine between the cups. [Shaar Hatziyon 473:18 in his second opinion]
 Admur 473:12 [See also Admur 472:15; 479:5]; Chok Yaakov 473:10; Maharam in Tashbatz 99; Ravayah 525; M”A 473:2; M”B 473:13; Kaf Hachaim 473:36
 Admur 473:13; Bigdei Yesha on Mordechai 22; Nitei Gavriel 80:3
 See Admur 182:2-3; 272:10; Ketzos Hashulchan 97 footnote 8; Ishkavta Derebbe p. 97; Shaareiy Halacha Uminhag 1:140; Piskeiy Teshuvos 296:9; Kitzur Hilchos Shabbos Supplements p. 67
 See Admur Seder 1:21; Luach 5:11; 174:4; M”A 208:24; Taz 174:2; Mordechai 150; M”B 174 and 206; Piskeiy Teshuvos 473:10
 Admur ibid, Parentheses in original
 Otzer Hahalachos 2 in name of Pela Yoetz “Haggadah” that the firstborns who fasted on Erev Pesach are to drink coffee beforehand; Piskeiy Teshuvos 473 footnote 49
 Admur 473:13; Chok Yaakov 473:11; Elya Raba 473:9; Shulchan Gavoa 473:8; M”B 473:16; Kaf Hachaim 473:40
Other opinions: Some Poskim rule that one may drink even non-alcoholic beverages between Kadesh and the meal. [Chemed Moshe 473, brought in Kaf Hachaim 473:40; Aruch Hashulchan 473:7 rules not to drink other drinks, aside for water, and only if he is thirsty]
 Admur 473:11; Tosafus Pesachim 103b; Razah 24a; Peri Chadash 473:3; Chok Yaakov 473:5; Aruch Hashulchan 473:6; See Nitei Gavriel 80:5 footnotes 11-12
Other opinions: Some Poskim rule it is forbidden to stop in middle of the Haggadah for a drink, once the second cup is poured. [M”B 473:4; Biur Halacha “Hareshus”; Shaar Hatziyon 473:9 Levush 473; Biur Gr”a; Ramban in Milchamos; Ran; Maharam Chalvah Pesachim 117]
 See Admur Seder 1:21; Luach 5:11; 174:4; Michaber 174:2; M”A 208:24; Taz 174:2; Mordechai 150; Aruch Hashulchan 473:7; Nitei Gavriel 80:2 footnotes 5-6
 The reason: Drinking other beverages, even with a blessing, does not appear as if one is adding to the four cups of wine, as the four cups are of wine. [Admur ibid]
 See Admur 474:3, and Poskim in Chapter 1 Halacha 4E, that the Al Hagafen said after the fourth cup covers all the previous cups of wine; Now, the law is that the Al Hagafen said over wine covers the Borei Nefashos of all other beverages, even if one did not include that beverage in the blessing of Hagafen said over the wine. [Admur in Seder 1:21; Admur 174:7; 272:13; M”A 208:24] Accordingly, he is not to say an after blessing of Borei Nefashos on any liquids drunk after Kiddush, prior to the meal, and is rather to wait and include it in the after blessing said after the 4th cup. [Admur 272:13 in parentheses; Ketzos Hashulchan 60:7 and 79:11; Piskeiy Teshuvos 174:4]