No, definitely get the treatment first. Insurance takes a while to go into effect, and you don't want to have to worry about what could happen in the waiting period. You won't get reimbursed for it, but tough cookies.
I researched testimonials and reviews of different insurance plans, and it seemed that the most affordable with the best coverage and customer service was PetPlan. I think the site is gopetplan.com, but you can just google PetPlan. I pay $25/quarter for each cat. $200 or $300 deductible with 80% reimbursement. Covers dental, illness, injury, and some other things. Also got a discount for having them microchipped with 24PetWatch. 24PetWatch offers a $20/year service that covers up to $3000 worth of emergency vet care if your pet is found and needs it. I'd say it's worth the $20. There's all sorts of preventative stuff you can do for your pets, you just have to keep and ear out for the new stuff and do your research. It's always well worth it in the end.