Good advise already given. For what it's worth, I've bass fished with a 6 wt quite a bit, particularly when it was the only rod I had, but now use an 8, 9 or 10 wt. The main reason I might bass fish with a 10 wt is there are Stripers in the same waters & I toss some really big flies sometimes at both. I've landed some 20-30" Stripers on the 6 wt, which are about an average size range that I might encounter but would not specifically target them with the 6. Most of the time an 8 wt is sufficient. The 9 or 10 can be very useful at times particularly as the wind speed increases or when further casting distance is needed or when using really big flies. I sometimes throw rabbit strip eels that may be 8-10" in length & once wet they get heavy.
An 9 wt would be a good compromise. You have to ask yourself, if you'll need the 10 wt, which should give you a bit more distance with bigger flies than an 8 or 9 and a bit more power for fighting wind. Otherwise, any of the 3 should easily handle all but the largest fish.
A 12 wt is as gator said, much more than you need unless you intend to only target the largest fish. Plus, it will get tiresome if you do a lot of casting. Keep in mind that those folks who may use a 12 wt, even for species such as Tarpon are usually sight casting. If you'll be blind casting, that could wear on you quickly with a 12.
As far as sinking lines, I own several in various sink rates, but the majority of the fishing I do is with a floating line, as most times I'm fishing shallow water of less than 10 ft. At that depth the only time a sinking line is any advantage is when there's a strong current. Beyond 10 ft depth, and particularly combined with current, a sinking line can be good to have when needed, but if you intend to get 1 sinking line, be sure the sink rate fits the waters you'll fish most so you get the most from it's use.
I never fly fish water deeper than 30 ft, at least not down to that depth. But between 20-30ft a fast sinking line has been beneficial at times. Between 10-20 an intermediate sinking line is what I use most, again except when there is a strong current. If I see the need to fish deeper than 30 ft, frankly, I would rather use other tackle.
As far as tapers, the lines I own vary, but all are WF. Because the majority of the casting I do is within 50 ft, I don't see much difference between the tapers with the same rod & fly. One line I have is an Orvis Salmon/Steelhead 9 wt line & another is a SA Striper 9 wt line ( might be the other way around, my memory sucks!) & frankly for me there is little difference in the way they cast.
IMO, specialized tapers are that way for a specific purpose, and beyond that purpose, there may not be much benefit. I own such lines because I got them a decent price, and really no other reason.