You have a ton of options--- all of them will work as far as catching fish goes and people tie them all kinds of ways.
For the body-
the traditional choice is Pearsalls silk-- But pearsalls comes on a small spool that won't fit standard bobbins, so that can be a pain. You may want to use it at some point down the road--- more as a nod to tradition than for any practical reasons. But for now, any floss will work including:
craft store silk,
synthetic floss like rayon. (If you use a 4 strand rayon floss cut a 6 " length and separate it into it's 4 strands and use 1 strand for the body)
or you can just use colored tying thread (orange, yellow, green and purple are traditional silk body softhackle colors-- you can just get a spool of 6/0 thread in one of those colors and use it as the tying thread and body all in one.)
Down the road if you get into tying and fishing soft hackles (and some people do) you can kick it up a notch by using the translucent qualities of silk. Some folks will tie an underbody of white floss, tinsel or another color of silk, and add a body of silk over it. When wet, the underlying color shines through the top layer of silk creating a pretty cool effect.
Other options for softhackle bodies include dubbing- like Hare's Mask. Some people tie patterns like "Hare's Ear Flymph" where the whole body is made of dubbing. Others use a wisp of dubbing in the thorax area on a pattern like the Partridge and Orange (but some people tie it without dubbing). Peacock Herl or phesant tail fibers are also used for bodies on many soft hackle patterns, and are wound on like the chenille body in a woolly bugger.
The traditional choice is a heavy wire wet fly hook like a Mustad 3906, 3906B or 3399A (less expensive hook) or equivalent--- but don't feel like you have to be limited to those hooks--- use whatever you have- dry fly hook, nymph hook, curved scud hook-- all can be-- and are -- used for soft hackles. Some folks tie them on dry fly hooks to have them ride higher in the film- others add a bead head to get them to fish deeper. (But if you tie it on a dry fly hook and decide you want to fish a little deeper you can always just add a split shot to your tippet.)
At this point I think you'll probably be using other types of hooks more down the road, so go with any dry fly hook or a nymph hook you have on hand rather than going out to get a a specific hook for wet flies at this point.
Some tie them without ribs, and it's perfectly fine to do so.
Adding a rib can help durability though, and in the case of wire, it can add a little flash too.
If you decide to use wire, you might pick something like fine diameter gold.
Another option for a rib that some folks use, is to leave a long tag end of tying thread (or silk if you're using that for the body) about 3" long or so hanging off the end of the hook. Wrap the body as you normally would, and then counter wrap the tag end of thread or silk up as a rib and tie off excess and clip the waste end just as if it was wire.
Some folks use a synthetic flash material like a strand of Krystal Flash for a rib to add sparkle (it won't add much as far as strength), plastic netting from a tomato or onion bag you name it.
The only other thing I'll add here is a bit about proportions-- and again it's more of a traditional thing with tying soft hackles. The body (and shank of the hook if you're using a traditional wet fly hook) typically is short compared to many other fly styles. If you look at most tutorials-- or pics of well tied soft hackles on straight shank hooks, you'll see that the body usually starts just above the hook point or mid way between the point and barb, and goes forward from there. Many other fly styles have bodies that start further back- behind the the barb in many cases. One advantage of tying them this way is that you can get away with using a larger size hook (with a bigger hook gap and stronger wire) for imitating small flies.
They're a great searching fly, easy to fish, and often do well as imitations of emerging and drowned adult mayflies and caddis and adult caddis that dive underwater to lay eggs after mating. And there is something about the simplicity of soft hackles that gives them a real elegance. Here's a good page to check out from Dutch tyer Hans Weilenmann's site with a bunch of his flies-- many of them are soft hackles or similar style wets. You'll see he uses a bunch of different hook styles (and all kinds of materials) to come up with all kinds of very well tied creations. Hans Weilenmann