I'm quite sure you can mix & match two single coils and a humbucker for the discounted HSS set price, call or email BKP to get the instructions to do so.
I like the open poled pickups, the covered ones sound great too and I would play them. I've owned both types, I don't really hear a difference as much as I feel a difference, but it's just a personal thing, as you see Steve Stevens uses the covered ones and he's a tone freak like us, so no worries or difference to speak of really.
I've been holding off on an opinion, after owning / playing / adjusting and really getting to know the BD in my HSS, I most surely would have the Slow Hands for my single coils. The BD has a low growl and a thick bottom, its highs are very clear and rich and do not lack treble. However I want the EQ on the amp to respond great for all my pickups without adjustment, so I realized why BKP matches this set up.
Crawler is a great set for you too, MM's or IT's or one of each might do, either way you're gonna love them. :)
WR