firstly, do intro yourself at the newbie thread. Then come to TT and become official member.
You have made a choice of the 1.9 e46. maintenance will entirely depend on you. e36 may have a higher maintenance and e90 may have a lower maintenance depending on the owner/driver/user.
engine wise, the 1.9 would be less of a problem as compared to the 2.0. whether it is under power or not, depends on what you want. of course the 1.9 can't go 0 to 100 as fast as a 2.5 or 3.0 etc. but the 1.9 can still do 190 comfortably as compared to other makes of 2.0's. Again depends on what you are looking for in the car. Whether more gas or not, also depends, some can get below 9km/l whereas others can get above 9km/l depending on the driver. but then again, 1.9 would consume less generally as compared to higher c.c's and btw, petrol prices are rising.