>linux
it has no custom firmware. I don't know what the official firmware is based on, but it doesn't look like any normal linux.
>install a type c port
most of the time spent doing that is going to be carefully sanding the PCB and plastic shell. if you get the USB-C kit from giltesa you are in for some pain as it does not fit properly and trying to put the plastic shell back on over it will cause it to rip off. if you buy the no-name chink kit then you will have to desolder and reuse some super tiny SMDs.
>japanese seller
make sure you get one that shows the screen on. a lot of japs leave their game consoles sitting out where the sunlight gets them and yellows the screen.
>new
they are all used. there are no new units anymore.
>worth it in 2025
love me vita, but I don't recommend it. I play vita games and old NES and SNES games on it.

there are a shit ton of brand new devices from china that are far, far more powerful, and cheaper as well. the Mangmi Air X is the newest best deal.