Install the faucet and sink before placing the counter top. You’ll be able to tighten with channel locks. Way easier than looking up. Into a dark narrow space.
Countertop was already installed. I bought a basin wrench but the new faucet had a plastic screw in sleeve thingy that tightens it (no nut) so it wasn’t needed.If the counter is already in bit they didn't install the sink, I would do faucet first and then sink. Same reasoning.
Sink and faucet installed as well as a over-the-range microwave. Inlaws are happy with the new kitchen and appliances.