Chad,
I know you've seen my rigs. On my fathom 30's, I run straight braid with a mono shock/rub leader. My 30's are holding 400+ yds of 65# braid and I typically start with 25-30 ft of 100# mono for the shock leader and replace this when it gets too short after numerous cutbacks etc from adding and removing rigs. Pinoyfisher gave you some great advice and I will add my 2 cents to what he said.
There are 3 basic setups not counting a shock or rub leader etc. All mono, All braid, or braid backing with a mono topshot.
I'm not gonna talk about #1 since that's pretty cut and dried. Depending on your reel and your casting ability/control is going to be a factor in what you choose to do. Each option will have some pros and cons IMHO and everyone will have different opinions.
All braid
This option will yield the greatest line capacity and can yield greater casting distance. Useful for those using a smaller reel. The smaller line diameter and decreased weight to length ratio can decrease the amount of drag and loss of velocity of the weight and bait. Of course this needs to be countered with good to great casting ability/control. This can be accomplished with either personal ability or cast controls on the reel(magnets or centrifugal). Lack of either will lead to many headaches and much frustration. Braid's limpness/lack of memory is the primary cause for casting issues and crackoffs. Since braid does not have any inherent memory, when you cast, the braid will not lift off the spool and start to "fluff" as mono will when the spool velocity is beyond that of the outgoing line. Braid can and will(especially when wet) start to reverse wrap on the spool. This will usually result in a rapid departure of your rig and weight from the rest of your setup. This is where the cast control on the reel is truly important, even if you are a very good caster, as it helps to prevent the spool speed from increasing beyond the speed of the outgoing line.
Braid backing/mono topshot
This option is a good middle ground. The braid backing can give you the increased line capacity and the mono topshot will help with casting issue. Mono, especially so in the heavier # ratings, can provide a measure of security against backlashes that cost you your entire rig. Mono, due to its memory/stiffness, tends to start "fluffing" for quite a while at the beginning of a backlash. Fluffing is when the spool velocity outstrips that of the out going line. Mono, with its stiffness, will start to loosen on the spool generating a number of loose coils. Typically, you can get quite a number of these lose coils before the reel actually birds nests. This is where your casting ability can be useful even if you don't have reel controls. At the first hint of a fluff forming, you have time to apply some pressure to the "side" of the spool to slow it down. With braid, by the time you notice loose line it is usually too late.
Now for some personal suggestions.
If you decide to go the full braid route, use an 8 carrier braid, not a normal 4 carrier braid. The 8 carrier will maintain a rounder profile and will not flatten nearly as much as standard braid. This helps tremendously in preventing the line from digging into itself, which will also cause a reverse wrap and breakoff on the cast. I personally use Sufix performance braid 65#. In the heavier sizes(50# and up) it is an 8 carrier braid, is not terribly expensive, and I have had zero problems with it.
Learn the FG knot, this is hands down the best braid to mono knot for heavy line when casting is involved.
If going the mono topshot route, estimate your longest cast and add 20-50% more mono beyond that.
