Everybody else covered the mechanics so here's my take. Make a starter 5-7 days ahead of time and plan on stepping it up twice. You're gonna need a lot more yeast but you can still get by with one vial or smack pack if you do it right.
I pretty much just doubled my ingredients when I went to 10 gallon batches years ago, but after a few batches you'll be able to tweak that to compensate for your system. I know that a 10 gallon batch of Imperial stout with 45 pounds of malt is much less efficient than a 5 gallon batch that may only require 18 pounds of malt.
There are advantages to larger bath brewing if you do it right and have the right equipment. It takes me 2 hours less to brew 10 gallons with my 3 tiered system than it did to brew 5 gallons with my single turkey fryer setup. I have twice as much beer, and as stated before I can make 2 different beers from one brewing session. The disadvantage is that I have twice as much beer to drink.