For 323, you could go the DINAN route, and do both the Engine and the Transmission software for your steptronic.
Or you could go with the Shark Injector, which many 323 and 328ers have, it has proven and reliable gains, and it can be taken off the car in 5 minutes, in the case that the car needs to be checked for a problem at the dealer.
the DINAN might run you 700 in total for both software downloads, the Shark is only 300, and you can take it on and off the car at your discression, i would probably go with the Shark, i hear it kicks ass and i wish they made it for the 325
As for floor mats, Dealer will have them... Circle and Pacific BMW offer the best OEM part prices, try www.circlebmw.com/
and as for alarm, all cars have the "clown nose" under the mirror, but the Alarm is a dealer installed option, that you must purchase separately from the car.