vengeance weapon battery - if you're using vultures and don't want to spend money on the dinky forgeworld punisher cannon model, i'd suggest you get a hold of the vengeance weapon battery's cannon as it's huge and rather stylish
Kasrkin/Stormtroopers/Tempestus Scions (all meaning the same, but the last one is what they're called now) can be taken in squads of five to ten, as the vendetta can only transport 6 models i'd suggest you put them in there, as the standard valkyrie can carry 12,which would be good for a standard toops slot veteran squad and maybe a commisar or priest.
Mont'Ka is a supplement book which adds in additional ways to use imperial guard - if you're going flyer heavy it alows you to take 3 units of valkyries/vendettas together and grant them special deployment bonuses.
If you're using forgeworld models, then by all means use forgeworld rules - they're accepted as part of standard play now since, frankly they're no longer the win button they used to be since the standard codex have more rich creamy cheese.