The length of the walls:
Minimum length:[1] The minimum size of a Sukkah is seven by seven Tefachim [57.2 x 57.2 cm], as explained in Halacha 6B. Thus, technically one should be required to have three walls which are each seven Tefach long. However, using the Biblical rules of Lavud, at times it suffices to have only two walls of 7 Tefach as explained in Halacha D, and at times even only one wall of 7 Tefach. This can be accomplished in the following way:[2] One has a single wall which is seven Tefach long, with another wall of 4 Tefach horizontal to it, within 3 Tefach from the end of the 7 Tefach wall. The third wall can then be made with Lavud and Tzuras Hapesach. Thus, it is possible to make a Sukkah with only one wall of seven Tefach. However, it is never possible to make two out of the three walls less than 4 Tefachim using the rules of Lavud and Tzuras Pesach.[3] Nevertheless, as stated above in Halacha A, the custom is to make three/four complete walls without resorting to the rules of Lavud.
Maximum length: There is no maximum size for the Sukkah, and hence there is no maximum size for a wall.
[1] See Michaber 630:2-3 regarding the rules of Lavud; 634:1 regarding the Size of 7×7; Sukkah 3a and 15; Piskeiy Teshuvos 630:7
May one make a wall using Tzuras Pesach? See Biur Halacha 630:2 “Sheyamid” for a dispute between the Ran and Rosh if Tzuras Pesach is a Biblically valid wall for a Sukkah. Practically, it is at the very least Rabbinically invalid.
The status of a Tzuras Hapesach in middle of Sukkah: If a Tzuras Hapesach is made in middle of a Sukkah, it is disputed as to whether it splits the Sukkah in two, and thus requires that both sides contain 7×7 and 3 Kosher walls for it to be Kosher. [See Minchas Yitzchak 10:50 who rules its valid; Piskeiy Teshuvos 630:4 in name of Poskim that perhaps it is invalid]
[2] See Biur Halacha 630:5 “Ki” in name of Peri Megadim; Piskeiy Teshuvos 630:7; However, see M”B 630:87 that one must always have a full two walls. Vetzaruch Iyun.
Other opinions: Some Poskim rule that a Sukkah is never valid unless it has two complete walls of seven Tefachim. [Chazon Ish 75:1; See Piskeiy Teshuvos 630:1 and 7]
[3] Ateres Zekeinim 630; M”B 630:6 that the Halacha Lemoshe Misinai is that only one of the walls suffices to have a Tefach pole