Saying Hodu: It is a custom established from the Ball Shem Tov to recite psalm 107 prior to the Mincha prayer. Hodu is omitted prior to Mincha Erev Shabbos which is also Yom Tov or Chol Hamoed. [Some communities are accustomed to recite Hodu together with a Minyan. This is not the Chabad custom, and rather every congregant recites Hodu on his own and the Chazan then begins from Ashreiy.]
Saying Patach Eliyahu: After Hodu one recites Patach Eliyahu. [Patach Eliyahu is recited even when Hodu is omitted such as Erev Shabbos Chol Hamoed.]
Tachanun: It is customary to omit Tachanun by Mincha of Erev Shabbos. [This applies even when Davening Mincha early by Mincha Gedola. Likewise, for this reason one who ate bread after midday does not recite Al Naros before Birchas Hamazon but rather recites Shir Hamaalos.]
Wearing a Tallis: Many communities are accustomed that the Chazan wear a Tallis for Mincha of Erev Shabbos. This is not the Chabad custom. Nevertheless if not wearing a Tallis will cause strife in the Shul one is to compromise on his custom and wear the Tallis for Mincha. However one is not to wear a Tallis for Kabalas Shabbos.
If the Minyan has begun Ashreiy and one has not yet recited said Hodu and Patach Eliyahu what is he to do?
One is to Daven Shemoneh Esrei with the Minyan and recite Hodu and Patach Eliyahu after Mincha.
If one’s Shachris prayer continued past midday is he to recite Tachanun?
Some Poskim rule Tachanun is not to be recited.
Is an Avel to be Chazan by Mincha of Erev Shabbos?
An Avel may be Chazan by Mincha of Erev Shabbos and so is the Chabad custom. However there are communities which are accustomed to not have an Avel Daven as Chazan by Mincha due to its extra holiness.
The greatness of Mincha Erev Shabbos:
According to the teachings of the Arizal the revelation of the holiness of Shabbos begins from the 5th hour of Erev Shabbos. This revelation intensifies with the prayer of Mincha. It is an auspicious time for the elevation of the soul, and for repenting on actions done during the previous week.
It is customary to Daven Mincha close to the entrance of Shabbos, after immersing in a Mikveh and wearing Shabbos clothing. One is to Daven Mincha with extra concentration due to its great level.
 Siddur; This custom is brought in Maor Eiynayim Beshalach in name of the Baal Shem Tov
 This psalm is said as a thanks to G-d that our body and soul have not been injured during the work of the week. [Shaar Hakolel , brought also in Ketzos Hashulchan 77 footnote 1; See Piskeiy Teshuvos 267 footnote 10 for other reasons mentioned.]
 As it is belittling of Yom Tov to recite a thanks to Hashem for removing us from the mundane activity of the week to Shabbos when Yom Tov is likewise not a time of mundane activity. [Ketzos Hashulchan 77 footnote 2]
 So is the custom of Polisher Chassidim. [Ketzos Hashulchan 77 footnote 1] Shaar Hakolel writes it is to be said with a Minyan in order to thank Hashem in a public forum.
 Ketzos Hashulchan 77 footnote 1
 Ketzos Hashulchan 77 footnote 3
 Peri Megadim 267 M”Z 1
 M”B 267/1
 Piskeiy Teshuvos 267/1
 Shaareiy Halacha Uminhag 1/57
 Ketzos Hashulchan 77 footnote 1
 Az Nidbaru 11/1
 Likutei Mahrich, brought in Piskeiy Teshuvos 267/1
 Kaf Hachaim 267/2; Piskeiy Teshuvos 267/1