Salt water will permanently kill a phone after it’s exposed to water inside the phone , phones are water resistant but not water proof. if your phone has water inside if needs to be opened and cleaned quickly before any corrosion begins or short circuits. do not keep trying to use phone hoping it will start working just doing this while it’s wet can zap circuits . Get it to a repairer and get it opened up for assessment but it dies completely.
It maybe just needs a reset, home buttons can be replaced they will just operate at a home button without finger print feature, I suggest replacing home button then you can reset it easily. if that does not fix then next step is to look at hardware make sure all plugs are not damaged and plugged in correctly and flex cables of new screen are not damaged. if still not joy it could be faulty screen try another , did your old screen light up try it and see if it still lights up. next step is logic board damage maybe back light this will require micro soldering to fix.
Sounds like there is still water inside your phone stop trying to turn on or charging as if there is water inside it can short circuit and zap circuits of your phone causing permanent damage. best option is to get the phone opened up and dried fully before attempting to power it up again
Your phone has water in side is at risk of zapping at any stage- stop using it! it needs to be dried out ASAP before you should attempt switching it on again, the only way to properly do this quickly is to have the phone opened up .
Make sure the circuit board is seated and screws are tightened correctly. below the circuit board are cooling pads if your main board is not seated in the phone correctly this can cause overheating. Also your cameras are not operating check to make sure they are plugged in correctly this could be causing short circuit and potentially overheating