I'll answer what I can but I urge you to research your questions as much as possible too
1. I don't think the body used or clothing was ever posted but you could PM the person who first posted the photo and ask. I'm not too familiar with phicens bodies but I suppose you could eyeball the bust size and
2. Check the height from specs of the body you are buying. If the custom you are referring to(I assume the tall thin one a few pages back) used a Phicen body, I don't think it will distort the proportions but just make it look thinner, unless they used a custom head.
3. They usually do yes. You might get hand pegs and ankle pegs with the body which will be usable with the hot toys hands. If the feet are part of the seamless body you will need to buy boots that are hollow so they fit on the feet of the body. These are available like most parts(check eBay)
4. There are plenty of alternatives but phicen are well known and used. You can check the general action figures section to read and ask for opinions on them.
5. Sure are. You should check some of the US websites that sell figures and parts, like monkey depot...
That's about as helpful as I can be, which I know is not much but
I hope someone else comes along that can help more