I start with a flat nylon collar - either actual buckle or more usually the kind with the quick release plastic clips where you squeeze the sides - not sure what the technical name is. For a leash, I use a 5-6 foot lightweight nylon or cotton leash when they are babies. I don’t usually care for nylon leashes but for babies I want something light weight that they are less inclined to chew than leather. You’ll need to start with a smaller collar than he will wear when he is older, too.
I don’t believe in harnesses - they just encourage pulling, which Labs tend to do anyway as they get older and heavier.