Well, to be kind of blunt about it, if you have to ask, Pentax will be more than 'professional' enough for you. If it turns out that another brand has something you can only get there, you'll know exactly why.
When I shot weddings, I didn't even use automatic exposure.
I think all Pentax may lack for the purpose is a lot of really nice high-tech flash system options. And if you're doing studio portraits, you won't be wanting proprietary flash systems anyway. But if you start on weddings, your first worry won't be lack of a two thousand dollar full frame body and equipment to match, it'll be being good enough to justify one as a business expense. (And staying sane.
)
Anyway, don't worry about where you are right now. If you'd spent the same money on Canon or Nikon and suddenly 'became pro,' you'd be wanting to replace all that stuff anyway.
For the most part, you simply don't need most of what makes those 'pro' cameras so expensive to shoot weddings. The likes of a K-5 has the important stuff for those purposes, and the durability and controls and excellent glass you do need. (And one thing is, fatigue is a factor. Five pounds of camera body that can blaze away at ten frames a second on some other job are still *just as heavy when you're flatfooting around someone's 'Special day at the Park Plaza.' *) What's more, the lack of dedicated pro service networks can be made up for by the fact that if your camera doesn't cost as much as your car, you can keep your own backups.
So, anyway, don't worry too much what Pentax is doing about full frame, a feature much extolled by people who never actually touch such a camera. (Don't get me wrong, I really wouldn't mind the viewfinder, myself)
Other developments in tech could make it moot by the time you ever get near one, anyway.
Any weddings or such I shoot these days are kind of like vocational rehab, if I start needing more camera than the Pentax name can provide, I'll call it a win and be glad to have been here.