They are the same exact console. The only real difference are the exclusives and the services. Do your own research.

Both have solid modding support. I'd personally go with the DSi since you don't have to rely on a laser. Really you can get both for less than $200.

150 euro seems a bit steep but I'd go for the ps4. It's still a supported console, meaning it has online features enabled, and it's easier to repair. I'd ask if the CD drive works, if it load into the OS slowly (that could mean the hard drive is dying), and if the controller has any drift in the analogs.

Probably more than a decade, but it will happen eventually.

Eventually the servers will shut down. The Wii can no longer use its features, same for the 3ds. This means that if you purchased a game digitally then you won't be able to re download when the console stops being officially supported.

PS4 emulation is still lacking, PS5 is barely even a thing at all. I'm sure they will eventually happen, but even the X360 emulation scene isn't that good. As time advances consoles get more and more difficult to emulate.

As the others said, disk. This is because eventually Sony's PS5 servers will go down and you will lose the ability to re-download games you've purchased to the machine.

As of now it's unknown if there will ever be a PS5 hack that will allow installation of games from non-legitimate sources.

It's always good to have physical copies.

"Portable"

I am somewhat doubtful of this thing. First off PS5 can't really game that well at 4k, but since they are the same price (which is sus) you might as well get the 4k one.

I want to see pics when this is done.