you also need to think about what format you'll be wanting to shoot. If you are on a budget, you get the most shots on a roll if you use 645 (16 frames) ... 6x6 square gives you 12 and less for the 6x7 and 6x9.
then you need to think about what type of camera - toy, tlr, slr, rangefinder, folder with/out rangefinder ....
If you're thinking of macro, then you'd probably prefer an SLR so you really see what's going on with DOF etc - something you wont get with the other camera types. As Francois says, the macro lenses are more pricey than the normal ones but at least with an slr you can buy the lens later on down the line to add to your system. that said, if you're more of an intuitive snapper-type, the MF Rangefinders are great, although they have a limted range of lenses (if they're not fixed lenses like the fuji ones) and they can be used with a more considered approach on a tripod too if that's what you want - you can get them made by mamiya (6 or 7 or 7II), bronica (RF645) and fuji (too many to list) in 645, 6x6 and 6x7 with all sorts of auto/manual/ settings.
hope that helps