What's the best Uma to go for the 26+ wins achievements in Career mode? And what kind of deck works best for that?

I have 25k carats right now to pull, but my anxiety is making me think about getting the $70 pack to hit 30k. Is it worth it? Or is there any chance I can reach 30k before the Kitasan banner ends? (I only have the monthly pass)

Realistically, how many carats can you get for free, (only counting the monthly pass as additional non-free content) in 10 days? I’ve only progressed through the story so far, but there are still a lot of trophies I haven’t cleared yet.