Would recommend simply locking out the front fork instead of changing it out for a rigid. Street tires. Then upgrade the drivetrain. Chain, cassette and chainrings. Replace your brake pads and cables next. Maybe replace your deraileur(s). If the lateral swing and adjustment screws are still good don't bother to replace, just clean and re-lube. Get some fenders. Either replace or repack your bb. Trial and error is the best teacher. I've got 3 different bikes with which I commute. They're all set up slightly different and 'feel' different. I just deal and keep pedaling.