In general 15" rims would be fine, but you have to go with a low profile tires then; which would mean slightly less comfortable, but better cornering due to stiffer sidewall.
@storm (the guru) had 15" rims on his Vitz 2003. 195/50/R15 (to be precise) with Pirelli Dragon as rims and Dunlop tires.
Michelin, Dunlop, Yokohama, Bridgestone; all these are reliable brands. But you must already be aware that there are a lot of varieties within a single brand. In short, jitna gurr utna meetha. You may also search the forums for post on tires alone.
@storm had a lot of explanation in this very thread about tires and the proper sizes. Check page numbers: 74,75,112,113 also.
Hope some more experienced and Karachi based member will help you about your other queries.
Bro, thanks...and i'll post a pic of that unit and its message ("Insert Correct Map Disc") in a couple of days. Going out of the city right now.