1) There's a footnote that says a Company Master can't take a bike. Of course, he could still join the unit, taking a jump pack to keep up with them.
2) Yes, this ability has already been seen in the Space Marine FAQ.
4) The Darkshrouds don't give each other Stealth. Not that you need it; Jink plus Shrouded equals 2+ anyway.
5) It says "boltguns," which are your bog-standard rapid-fire bolter. That's not bolt pistols, and not storm bolters, but would include the bolter part of a combi-weapon.