CAn't help you with the year of the bike, but I think that the Mesa's switched over to full-suspension after Pacific took over Schwinn (might be wrong). If it is a full-suspension Mesa, then it is definitely a newer model. If it is hardtail, it might be.
Don't plan on putting a mini-pump in or attached to the seatbag. I currently use a Specialized seatbag that is a bit big but carries everything I need. Pedro's makes some nice smaller ones that are just big enough to carry the essentials (And use recycled innertubes!)
I use a Blackburn min-pump. I bought it a while ago for $15 bucks at my LBS but it has lasted over two years of hard riding. I have always had better luck with Blackburn products than with the stuff made by Topeak.
Do your valves come to a point or are they short and flat at the end. An easier way to figure it out is to look at the valves on a car tire. If the valves look that same as though on your bike than you have a type known as Schraeder (short and flat). Presta valves come to a point at the end and have a small nut that it tightened and loosened to allow for the valve to be opened. Make sure to get the tubes with the same type of valve when buying spares. Your rims are drilled for the type of valve that the bike came with. Schraeder valved-rims will have a larger hole than rims originally drilled for Presta valves. You can use a presta-valved tube in a rim drilled for Schraeder valves in a pinch, but don't ride it for too long as the excess space around the valve can create a "rub spot," eventually causing the tube to flat. Schraeder-valved tubes cannot be used in rims designed for presta valves unless the valve hole in the rims if drilled wider.
I wouldn't worry about the brand of tube you are using unless you are looking to do some tough downhilling or are really worried about weight. The brand that the LBS stocks is fine for most applications. If you have a problem with flatting and you can narrow the cause down to how hard you ride, you might want to try a thicker, heavier tube to be more resistant to flatting. Running your tires at the correct pressure will go even farther towards minimizing the number of flats you get.
-Moab