Question for a car mechanic or just someone who knows a lot

right now i have a 2002 subaru outback base model, and had a few questions. in the car i have right now, i have 2 12inch 800w subs and a 800w amp in my car connected to the battery. i know i’m only getting 400w per sub since the amp is only 800w.

i wanted to add a converter to be able to plug in something like an xbox or multiple phone charges or something like that, and would have to connect to the battery as well. i dont want to overload the battery so my question is, if i got a high performance alternator for my car, would i be to run more electronics in the car so to speak?

another thing is, the converter i have in my car is a continuous 300w and peaks at 600w and i know i probably won’t get all 300 just plugging into the cigarette lighter. would you think this would be enough plugging straight to the battery if i got the other alternator, or you think a stock car could run that as well as the amp?

You should be fine but to be on the safe side I would get a more powerful alternator.

the car’s stock alternator is at 90amps, 160 should be good yeah?

i was going to add 2 head rest screens as well or just 1 overhead one

160 would be fine just make sure you get the right pulley to match the output.