What is the source for people getting drunk on Simchas Torah? Is it the correct thing to do? Based on what the Kitzur Shulchan Aruch says I would assume that since on Purim (where it is an explicit halacha) one is only allowed to drink if he wont miss or desecrate any teffilot or mitzvot and only if he wont act improperly, how much more so on Simchas Torah where (1) it isnt mentioned as an explicit halacha and (2) where we dance with sifrei torah and have lengthened tefillot one would be in the wrong to get drunk and go overboard with the alcohol. Would this assumption be correct?

Getting drunk is the Mitzvah of Purim, not Simchat Torah. Chabbad have the custom to drink a Lechayim of "Mashkeh" during Simchat Torah as a sign of Happiness and joy but definitely not getting drunk. (Otzar Minhagei Chabbad, Tishrei; p. 370)