Hi!
Personally, I'm a big fan of power weapons at the moment. Maybe consider magnetising 2-4 for the 15? Swords, axes and fists are all pretty great, and the first two are really cheap. If you're limited to a few magnets, definitely glue on the jump packs, at 1 wound getting
DC into combat is worth the 3 points. Plasma pistols are also very good for 7 points (I think there's one in the kit?) so give that some magnetic love