Well...if you're going to get something that goes that low, you need a good cabinet.
A 12 won't push that bass too well, you need a 15...maybe a couple of them, to get a good clear sound. When I play that F#, which is rare, it sounds like someone passed gas...just flattering, but you can hear a little tone in it. A good tight 15, with some 12s and a 10 will sound better, I'm sure.
I haven't changed my strings, since I bought it...but I just ordered some Conklin SIT strings...cost me $96 dollars with shipping. If you plan to string your 7 F#-C, be prepared to pay about this much. I haven't seen any sets that sell an F# string, so I had to buy a single, which cost about $26 dollars by it self!
We guys who play 6+ strings should check out the
extended range bassist's site. They have a lot of good information on there, and you can also ask the same questions.
I went with their suggestion for my lowest 3 strings, they're wider than normal, which is suppose to give a more solid bass, while the upper strings (D-F), are smaller than normal...normal being mediums. I also bought stainless-steel, but I like nickel better. Everyone there talks about stainless-steel, so I gave them a chance. The 8 came with stainless-steels.