What's my best boil size?

I’m an extract/spec grains brewer (about 20 batches). i have a 5 gallon brew pot and usually make 2.5 gallon batches (I use a Star Burner).
My question: Would starting my steeping with 2.5 gallons of water be better than using less water? (I used brewersfriend.com for my calculations.)
Also, I’m thinking about beginning to use later additions than just dumping all of my extract in at 60 minutes. Comments on that?
Mitch in Eastern NC