Welcome Andrei! The E46 M3 is in my opinion the perfect car BUT I am very biased :-) You will have to be very patient to find one in your budget if you want a sub 100km car and later than 03. White is going to be very hard to find on the later model cars also. I think white is the perfect color but have never found the right combo of color, interior and km's when I have been searching for one. As for as SMG vs Manual, you'll get all sorts of opinions here and on the other forums. It really comes down to personal prefrence, drive both and make your mind up from there. I have had both SMG & Manual M3's and really dont have a favourite and I grew up very much anti auto and thought all performance cars had to have a clutch pedal.
If you need any advice or answers to any specific M3 questions send me a PM, I know them inside out and I am only too happy to help out another enthusiast!