Well you've selected the same camera I've been looking at too. The Alpha a700 would be a great starting camera for you. Great for the new learner and advanced photographer. I always thought that one sould buy a camera with more than you need now and as you advanced in you're ability you won"t need to buy another camera too soon. As for lens, because Sony uses the same lens mount that (Konica)Minolta used, there are more than enough lenses that you may choose from. Adorama and B&H Photo have great selections of Minolta and Sony lenses new and used. Good shooting!
Not exactly true, I've seen many people who gives this reason and end up not being that interested that much into photography or ended up not using it cause they feel it is too much for them. Really pissed me off when they just leave their 50D in the cabinet to rot
Well, it is true that Nikon uses the same sensor as Sony (well at least in the D3x) but see the image comparison, Sony noise at higher ISO is the worst of the bunch, all blotchy, lose of details, high level of chromatic and luminance noise. So even if Sony uses the same sensor as Nikon, their image quality still suck at higher ISO so there must be something else. Like how the camera process the image?
Also, frankly speaking, most 3rd party lenses is not as good as the lenses produced by the camera body manufacturer and I kept hearing horror stories about 3rd party lenses always have problems here and there and need to be returned, there are good 3rd party lenses out there just we must keep an eye about the problems we might face I guess.
Another point to be taken is ergonomics, most ppl end up bragging Nikon is better then Canon or Canon better then Sony partly come from their experience in ergonomics, I frankly cannot be on Sony side even its true that their camera offers value for money cause I HATE its ergonomics, so that totally rules thing out. I'm okay with Nikon and Canon ergonomics. (well I guess I don't need to tell that I hate Sony high ISO performance too)
Now to answer the OP question, if you want to use a 18-200 lens, I must say for you to get a Nikon D90 with that lens instead cause if I'm not mistaken, Canon 18-200 is not as good as Nikkor 18-200.
Well I gotta be frank, when I look at Canon lenses, I only care bout their L lens and their primes, the only EF-S lens I have an eye for is the 17-55 f/2.8 and another wideangle zoom (don't know much bout wide angles cause I rarely need to shoot at wideangle). The cheapest L you can get is 70-200 f/4, the constant aperture is what make this lens great (maybe will interest you cause you mentioned long distance shots) though, if you do own a 70-200 f/4 maybe you will need to get a cheaper body like the Rebel XS or XSi which are fine camera bodies also (the small grip usually will make people not to like the Rebel series, so be sure to try it out before owning it).