It's your house -- you can try what you like.I have some milled lumber from a large red pine I cut down to build my road, might try to use that?
If you're going to be using the countertop for wet things, then pine might not be the best choice. But if I assume correctly, it's free wood, and large pieces of wood tend to look nice, so there's no harm in trying it.
Pine tends to warp, twist, and split as it dries, so make sure it's fully dried before putting it in.
Personally, I think I'd want something more durable.