Take heed to kingofsp's advice.
It really just depends where you're going to focus your effort.
If you're just trying to see what you're capable of, it won't hurt to test with a product-specific domain. Or, if you have one popular product in mind, and you don't think you'd be able to rank for it with just one page alone, it wouldn't be a bad idea to devote one site, with a product-specific domain, to it either.
Otherwise, a niche specific domain allows you to cover various different products, and depending on the competition, you might be able to rank on the first page of the search engines with one page/post/topic devoted to them anyway.
If you're going to buy longtail keyword type domains, you'd be better off purchasing a multitude of them so that you can rank #1 in google for each longtail, which would allow you to create a small network that ultimately benefits your hub site (which is at the product-specific or niche-specific domain). Most of the time this is unnecessary, but it's a possibility nonetheless.
As for backordering, yeah Godaddy supposedly sucks. I haven't tried them for backordering myself though, so I can't necessarily give a personal opinion on it w/ any experienced weight.
On the last day of the pendingDelete status, you can try catching the domain between 12 - 4 EST. If it's a .com, it'll probably get snatched up though, unless you're quick to catch it just as it drops. I've caught a few domains at around the 2:40 EST mark (if memory serves me correctly, that is), so it isn't entirely impossible. It's been a while, so some things might have changed. For professional backordering help, you could always try Snapnames or Pool.
