Well you may have a case of thermal phimosis. It's simple dude :p The ribbon has been partly shorted out due to the water damage. With the charging port I would go for the same concept. Remember that water doesn't necceserily damage until it reaches certain temperature due to its composite density. When you charged it the first time it was enough to ruin the rest of it.
The issue would definetly be that the new chargin port is not authentic. Many fake parts are good but the price shows it all. You will need to buy an original port. Else if it's not the case, then either the wire is fake or how you assembled the port in plce.
It's ok to take out the antenna as long as you put it back properly. You've done a lot of good stuff but the problem still persisted. I would have changed the wifi and cellular antenna but would also check the SIM card slot. Maybe it's worth a try
Kinda hard to answer but first thing witch comes to mind is either ram or mobo. You should try memtest for the ram If all is fine with the ram I suggest taking a look at the capacitors on the motherboard to check for any leakages or inflated capacitors.
One good tactic is to soak the LCD in distilled and water and dry it. When it is completely dry soak it again in ethanol and leave it to dry either in a bag of rice or cotton towel. This will clear most residue and unwanted elements. But I have a feeling you would have to change the LCD. Good luck Joe