The 12" will show you lots of good stuff
maybe wait a little while before shelling out more on some kits from the many on offer , the eyepieces that come with your new scope will do a similar job and give you some time to figure out whats important
to you visually, personally I find a 160/110/ 70 X spread is good enough to deal with many dso, 110x or 13/14 mm in a wide field gets a lot of use imo in a 12", and is where I'd spend some dollars first up.
cheers