portraits, weddings, macro, nature, wildlife, and just random fun photography.
Portraits - much of this will be in the lens and in the lighting control; in fact indoor or outdoor you'll be wanting more lighting gear from simple reflectors and excluder to flashes and backgrounds and more.
Tends to favour good lighting - then good glass - then a good camera body
Tends to favour fullframe (35mm) bodies; esp indoors.
Weddings - pretty much as said for portraits; however camera body is possibly a step above the lighting (only just) because much of the time you might simply not be able to use it. Also note this is a very demanding area of photography (you get no repeats)
Macro - lens followed by lighting followed by camera body. In fact with your typical macro shot camera body isn't really that relevant; the lens setup is as is controlling your lighting (again can be simple or complex flash). Also some styles call for a good solid tripod support system
Nature - to generalist to give specific guidlines
Wildlife - favours good field skills above all else; followed fast by high grade long lenses (sadly these are going to be expensive, this is one area where you can't easily get by with cheap gear unless your field skills are top rate). Lighting setups tend to be far more simplistic.
Favours crop sensor cameras -
General order would be lens - camera - lighting; with a focus on the camera wanting fast AF and good ISO range.
In general there is only one camera body that will do all the above to an idea standard - the 5DMIII. Cut down from there can you can cover it all with a 7D and a 5DMII or 5D. Either way weddings and portraits will benefit a lot from the 35mm fullframe body, esp since it means you can shoot photos indoors with telephoto lenses (Eg a 50mm) without having to move back too far; on crop sensor you might find you have to work with wide angle lenses (ie almost anything shorter than 50mm), but these introduce distortion on your photos (bits closer to the camera get enlarged over those a little further away).
My general advise is to always go for the camera format you want first - I'd suggest considering a 5D original (second hand/reconditioned) if you are on budget. If you've more cash then you've got the 5DMII (second hand also an option). If you've more money to burn then the 5DMIII is ideal - giving you all the lowlight and fullrame bonuses, whilst also having an advanced AF system for the wildlife parts (the 5DMII and 5D have much more basic AF - still very usable, just not as good).
However look at the other points - lighting and lenses. Top rate lenses, even on a rebel camera body can deliver great results and you'll see far more gain in optical quality and clarity with good glass than you will with a good camera body (in fact cheap lenses on higher end bodies can appear worse than when the lens is used on a lower end body).
In the end I'd say if you want to go full-frame make the change sooner rather than later and then you can build your working lens line up around that body. For portrait work the 35mm body and pushing toward lighting gear would be a good start - lighting letting you control the scene and the light that you have to work with.