Correct me about brining recipe

Personally I'd cut the salt back a tad more but I've never brined salmon so there's that.

If it's enough to thoroughly cover your meat by an inch or so, sure. You need enough brine to completely cover your meat. However much you need, just make it in the proper proportions. It's less about the absolute amount of brine and more about getting the proper proportions of the ingredients in the brine and making enough to cover your meat completely in the container you'll use.

You could even start with a quarter recipe. If that's not enough to cover by an inch or so in the container you want to use, add another quarter recipe. Keep going until you have good coverage.