for a starter armor Kut Ku is pretty good, as it gives AuS (you can gem in AUM though), it also has a health boost, which is nice at the beginning as the kitchen boosts aren't too good early on.
as to what armor you should make next depends on your skill and on how far you can manage to get with the Kut Ku armor... I'd recomment you to look at the wiki, it has a pretty good list of the armors and what skills they have.
i haven't been using bowguns in unite so i can't give you any recommentations on weapons...