Hmmm... well, personally, I've never bothered with the "Pinning" rules, but YMMV. Some people love them, as they make autofire very tactical, but they're just not really my cup of tea.
Grappling, as in all game systems, can be a little wonky. If you think your players are gonna get in a wrestling match, read up on it.
Auto fire works differently in various lines. In early lines it was almost always the right call (+20 to hit, one extra hit per degree of success), but later lines like Only War actually made it harder to hit with a full auto burst with the trade off being an increased chance for multiple hits. Pick whichever version you think is cool.
If you want to be gentler with any Psykers in DH 1e, consider allowing them to use the fettered, unfettered, push rules from Ascension. I don't encourage that though, Psykers are supposed to be a pain-in-the-ass.
Oh, yeah. If there's a psyker in the team, pre-generate a Daemonhost. You'll thank me later.
Do you know what line specifically you'll be playing? Also, glad I could be useful, friend. I hope you have fun with your campaign!