Just looking for advice, what is he worth for studding to?

Wolf #34291 - Columbine (lorwolf.com)
Also, if I breed him can I still add on markings?

It looks like right now, studding prices for Zerdas range from 50MS-125MS
I'm personally still figuring out ideal price ranges for stud listings myself, so don't take my advice as the advice of someone who knows what they're doing, but I'd guess somewhere in the 50MS-75MS range for him as he is currently. Once you get the Merle markings on him, you can probably bump that up.

I'm not sure how breeding cooldowns or stud listings might affect markings, so if you're asking if you can add markings while he's listed or on cooldown, I've got no clue. If you're asking if breeding him at all will lock his markings/make his marking permanent, I'm fairly confident that's not the case.

I grinded for days to get hte Zerda applicator and studding him out could speed up the process for getting him markings and a mate for myself, but I'm scared it wont let me add the markings because I've never done this before

I was pretty sure, but I wanted to double-check for you. I've got Harrison, a wolf I've got project plans for, and I realized I had enough to buy one of the markings I want for him. I just bred him a few days ago (just long enough for the pups to have been born) and he's still on breeding cooldown.

He originally had a Timber accent and I was just now able to change it to a Cozen accent, so you should be totally fine to be able to change your guy's markings once you get the patterns!

It's possible that it may make you wait until he's no longer listed for studding (I'm not sure, that's just a wild guess), but I can confirm that breeding a wolf doesn't lock in their markings!