Digitizer sometimes stops working

For the wifi issue: you may want to follow this guide to locate the wifi antenna, and clean/re-seat its connection to the motherboard. It isn't incredibly likely that this will fix the problem (because toggling wifi seems to fix it also), but if you're opening the phone it may be worth investigating.

For the digitizer issue: you mentioned that the problem goes away with pressure applied to the top right corner. Since that area is where all of the display cables connect to the logic board, you may want to open the phone, re-seat those cables and see if the problem still persists.