My 2001 Galant ES V6

So, i'm not on here bc i need help fixing the wiring to my rear speakers, or how to fix anything, well kinda to fix things but.....

I am wanting to do upgrades to my car, and i haven't been able to find anything really productive to do so! this is the best i have found so far!

i'm pretty new to Mitsubishi.... i had a 90' celica for 4 years but i just ran it to death....literally!

but if anyone could help out, i would appreciate it!

i'm looking to get 19" rims for it, but don't know how to choose them!
as well as the looks of the car, i was also wanting to do minor performance upgrades over time as well!

so, i guess a ? would be, is there a certain way to pick out rims for my car? is there a size that i shouldn't exceed..... i want no more than 19's, and that's pushing it!