Replacing pex water line...Any advice or hints

Just make sure you use brand name fittings and have a good crimp tool. A "go-no go" tool is a good thing to have on hand and they are only a couple bucks.
I've used both crimps and Shark-bite fittings. For simple, easy to reach spaces, crimps are favored over Shark-bite. Most folks are baffled by plumbing so they choose the easier Shark-bite route. I would have no problem crawling under your house with torch in hand and sweating in new copper.