When you get him (after he is at least 8 weeks old), take him out every hour or so. Don't "let" him out: Go out with him, make sure he does his business, and praise and treat like crazy. In addition to regular trips outside, take him out when he:
has just eaten
just woken up from a nap
anytime he comes out from his crate
anytime you see him getting hyper and bitey, or whinny
anytime you seem him circling and sniffing the groun
For the first week or so after he comes home, set your alarm to get up and take him out half-way through the night.
Watch him closely to figure out his schedule - at first your job is to just take him out often enough that his need to go coincides with being outside. Then as you get to know when he normally goes, you can adjust your schedule of potty breaks to coincide with his needs.