Don't waste time getting a master services agreement reviewed by a lawyer, because big clients are never going to let you use your own master anyways.
Do talk to a lawyer before incorporating with multiple cofounders, because you need vesting. Do not mess that up. It is a big deal.
Don't waste too much money on company formation, though. Try to keep the transaction with the lawyer focused solely on vesting. There are lots of other things you can do suboptimally during company formation, but they aren't going to matter so much that you should spend extra money today to deal with them.
Do talk to a lawyer before signing your first employment agreement, but don't do it until you actually need to do that.