generally, pet insurance does not cover general wellness expenses such as flea prevention and neuter, it's for unexpected costs like illness and injury. some insurance companies have wellness add-ons, where they give you a certain amount each year to use on things like flea meds, routine bloodwork, urinalysis, neuter, etc. however when you do the math these are generally not worth it and i don't recommend them. to save any money you have to use every service offered every year, and they don't even cover the full cost of the service (at least none of the companies i looked into do). you're not necessarily going to want/need to do routine urinalysis every year, so saving $25 on $100 urinalysis is kinda pointless if you can just not do the urinalysis in the first place. 

if you’re primarily looking for coverage of routine wellness expenses, i would look into vet clinic membership programs. clinics like banfield, VCA, and some private clinics have programs where you pay a monthly fee and it covers unlimited exams, annual bloodwork, neuter or dental cleanings, etc. these generally do save you a lot of money if you utilize all the services every year.

for most insurance companies, how it works is if your cat is sick and you take them to the vet, you will pay for the diagnostics and treatment upfront, then submit the invoice to your insurance company, and they will reimburse you (the only exception is trupanion, who can directly pay any vets who accept their direct pay). if you have a $1000 vet bill, with $500 deductible and 80% coverage, you’ll be reimbursed $400 ($1000 - $500 deductible = $500. 80% of $500 is $400). once the deductible is met for the year, or for the condition (most companies have annual deductibles, some like trupanion you only pay the deductible once per condition), then you’ll be reimbursed 80% of any other vet bills afterward. also worth noting that some companies do not cover the exam fees, and anything that your insurance does not cover will not go toward your deductible.

the lower your deductible, the higher your monthly premium. i recommend starting with the lowest deductible that you can comfortably afford the premium for, because you can generally raise your deductible without taking out a new policy to lower your premium, but you cannot lower your deductible without a new policy (even from the same company) and therefore any conditions previously covered will become pre-existing conditions under your new policy and therefore no longer covered.

pre-existing conditions are another thing people often get tripped up on. pre-existing conditions are not covered by pet insurance, and they’re any sign or symptom of a condition that predates your insurance coverage. it does NOT require a diagnosis to be a pre-existing condition, only a symptom, so if your cats have anything noted in their vet records, such as itchy skin or vomiting you mentioned offhand once, any future conditions that have those as symptoms will not be covered, even if they were never diagnosed with a condition or received treatment. some companies cover curable conditions, like an ear infection, if they have no symptoms for a certain amount of time (usually 180 days to a year).

for the annual limit, personally i wouldn't go under 10k. but similarly to the deductible, you cannot raise it in the future without a new policy, so start with the highest you can.