i haven't really referenced the corset thread here, but I've done a lot of research and made several myself. If you want bust support and don't want to have to wear a bra then an overbust is your best option. I don't know that you'd want to wear a bra with that, a well made corset is as supportive (if not more so) than your bra would be. An underbust would allow you to wear a bra, depending on the top line you might get a little bust support from it. One of my underbusts fits under my breasts and is curved to match their shape and I get nice lift and support from that without a bra (I'm only a c though so I don't know how that would work out for you) and, if you're concerned about your nipples showing through stuff then the corset wouldn't help with that (apologies if that seems vulgar, I just know it's a point that matters to some people).
You'll probably be happiest with steel boning. Flat steels are more rigid, spiral steels offer great support with more flexibility (i find them more comfortable). Because Spirals have more give they work better for very curvy areas (up the front if using an underbust, and the side if you are curvy, and the back (mine has a pretty distinct inward and outward curve that makes flats uncomfortable). You can choose according to your preference or do a mix of both. If you choose to go with spirals you will have to use some flats along the front (if using a busk) and in the back by the laces for support. They come in a variety of sizes from 1/4 to 3/4 of an inch. Bigger steels = more support, I like the 1/2 inch ones the best as the 1/4 in ones are too flimsy. If you're a larger size you'll need to avoid the 1/4 or you just won't get the support you need. If you're making this as a foundation garment you'll want to go with the slightly more rigid steels over plastic because they offer more support, shaping and they just last longer. Cable ties (or zip ties) are a reasonable option for use in corsets that aren't meant for real support and seem to work better for smaller women/women with fewer curves. Do not use ridgeline (might have spelled that wrong) or another thin, cheap plastic alternative - it will not last or give you support. It will bend as you move, and after sitting in it a while it will develop permanent bends in the front that do not look attractive at all.
As far as fabrics go: Cotton is a good idea for an inner fabric. It wears well, it's comfortable against the skin, and it's pretty good at wicking away moisture from the body. It's also not too expensive, doesn't have a lot of stretch, and you can get it in a lot of fun prints and colors if you're into that sort of thing. Canvas/Duck can be used for the inside of the corset, but coutil (I've seen it written cotton coutil as well) is a better option. It is thinner which allows for thinner seams that just look better, and it has absolutely no stretch at all. It is more expensive a yard (about 20-35 USD) but it's a good investment. The key thing for the strength layer of the corset is that it doesn't stretch AT ALL that is your strength and support for the whole garment. I have used canvas in the past and it worked fine, however the seams were a little bit bulky. If you are larger or want a heavier corset you can use 2 layers of your strength fabric. you can use whatever you want for the outside layer of the corset, just don't get anything with too much stretch. If it does stretch at all (even a little like twill) then you'll want to use fusible lining to fuse it to a fabric that doesn't stretch (like your strength layer of coutil/duck) or a layer of heavy cotton).
Other things you might want : bias tape maker - some construction techniques don't require that you bind both edges of the corset but some do. This makes finishing the edges in an attractive fashion easy.
Grommets- these are stronger than eyelets. You'll probably want an awl or a puncher to put the grommets in (Depending on your preferred method). And a mallet (I like a nice rubber one since it's not too heavy and doesn't beat my grommet setting tool to death)
Something to set grommets with - the handguns aren't that great in my experience. You can get a large press that fits on your table but those are very pricey. I use a tool specifically made for my grommets (it's kinda like a heavy steel version of the tool that you can get to set eyelets with at your local fabric store)
Channeling - you can make your own or you can buy pre-made channeling to put the bones in. It's not too expensive and it can be easy to work with (it's a lot like underwire channeling in bras
Laces- corset laces are like heavy shoelaces, and they last longer and are stronger than using ribbon (but ribbon is pretty and can be used if you want to)
(Something to put on the ends of laces may be needed if you don't buy them pre-made)
Walking foot - I've never used one but I know some people like them for corset making because it can make keeping those thick heavy seams nice and even
Bones - your pattern (if using one) should tell you how many you need. You can buy them in several lengths and pre-tipped but you may need to cut them to fit your needs. Spirals come in cut lengths or you can buy a roll of several yards and cut them down yourself (Last time I checked this is a little cheaper but a bit more labor intensive. You'll want something to tip the bones with if you're using steels to keep them from getting too rough on your fabric. You can buy tips from your corset supplier or you can use tool dip/plastidip (never used this but I've heard good things)
(You'll need tin snips to cut bones, a file to round and smooth the edges of flats, and pliers to keep purchased bone tips from sliding off)
Busks - these come in a wide variety of lengths and several different colors
Before you make your corset you'll probably want to do a mock up. Muslin is pretty good for this, and for best results you'll want to add bones to it. If you don't want to buy all your real supplies up front, cable ties make a good mock-up boning alternative. Some people will use their coutil/duck for this, but I prefer the muslin because it's so cheap if you screw it up.
I'm sorry for writing a novel, but that's pretty much what I know in a nut shell. I really enjoy the Corsetmaker's community on livejournal.com. there are a lot of people there in various skill levels that are willing to offer help and advice. You can also hear pattern reviews, talk of construction techniques, and tips for drafting a pattern/modifying a pattern to fit you, and reviews of stores that sell various corset nessecities and pics of corsets in various stages of construction. If you don't want to join the community, you can still go over to their community page and the memories list has links to posts on just about everything you could want to know about corsets
. And it will let you look for targeted information as opposed to the mishmash of info on that long thread. I hope this helps and good luck on your corset.