Hey man!
FON!
I don't own an RS4, have a RS6 C6, but my dad has a b7 RS4 that i drive a fair bit... having had EVO's and skylines previously i'll try my best to get across some comparison and buying information.
I'm sure someone with deeper knowledge will give you a better in depth "buyers guide" but for now.
The RS4 drives lovely, out of the RS6 and the RS4 the RS4 really is a much more fun car to drive and to have fun in, depending on your EVO's power i think you'll be a tad dissapointed with the overall speed/Accell comparison as imo the RS4 (he does need to get a carbon clean though) lacks a bit, but as a family car and a comfortable car to drive around in its a box ticker on all levels.
Space inside will be similar to that of the EVO, it will be nowhere near as "raw" and you'll not get the same buzz from the b7 as you would the EVO especially round a track, it is a fantastic car in its own right but Audi's being Audi's are sensible and German.
Things to look out for really i couldn't say too much, but Carbon build up on the intakes is common, clutch pedal switches can also be an issue and brakes can be expensive if you don't
Shop around, also try find one that's had all its bushes/ball joints etc done as from Audi this is around £2000 for a full front bush/joint kit.
Look out for a notchy gear selection from cold (hard to get into first gear) this can sometimes be a sign the clutch is maybe not gonna last too long.
Oil pipes on the front end and the Auxiliary cooling radiator are also common to leak/corrode so its worth checking out if these have been replaced.
You cant really check without taking the bumper off unfortunately.
Personally i wouldn't let millage be a put off unless its not got the history to back it up, my dads is on 73k and its got thousands and thousands of expensive Audi receipts, car is perfect he's done 10k since he bought it with no problems.
All we've done is change the oil and filter, fuel filter, gearbox oil and diff oil...
As for options and advice on which model to look for etc your better off taking advice from the rest of the B7 page, my dads has heated front and back seats, comfort electric fronts, piano black inlays, flat bottom wheel and sunroof.
Hope that helps a bit and sorry to anyone if i was wrong in my advice!
P.S your EVO is stunning!