1) no :-) In fact keep abs away from uv - it doesn't like it.
2) my only advice on ender 3's is to NEVER buy one. Other than that watch any of the several million videos on youtube on how to totally rebuild them to actually make them work :-)
3) actually yes. 3d printed parts can even be stronger in some circumstances than injection moulded parts. A lot depends on the material and the orientation you print it in and the print settings you use.

Absolutely you can make tools - I mean don't expect a plastic spanner to be able to undo something like car wheel nuts. But for moderate use, they can be pretty good.

Pet-g is a total bastard to get good pruints from, but it IS worth persevering. Get the print settings right and you can make some incredibly strong parts.
If you upgrade your hotend (let's face it, at some point pretty much ALL the bits of an ender 3 will be replaced) you'll even be able to print with polycarbonate. But you'll need a hotend rated for up to 300c first.

And before you ask - I've detailed the problems with ender 3's and creality i3's in general several hundred times on the forum - just look around :-)