A nice 5 gallon starter should be fine if you are using the whole pack.
Dry yeast don't normally need a starter due to the large amount of cells
in a pack. Using a full pack in a small starter would deplete the built in
Even a 11.5 gram pack isn't enough to pitch if you pitch into cold wort.
At least not ideally. I don't think I'd brew a 10 gallon brew without
enough yeast to do the job with.
I usually make my starter a week in advance, so I have enough built up and let flocc out so I can decant the spent beer on top.
How do you BBQ an elephant....first you get your elephant....