Definitely get a pair if getting kittens.
Don't despair- I've had a dozen cats from various backgrounds over the years and only one has sought to ruin my household furnishings!
Plenty of scratching posts and you should be fine. Do a search on comparison websites for pet insurance.
Depending on the cat, because like people they have different needs/appetites, I would expect to feed each cat 1-3 packets of wet food per day, plus some dry food. Do a calculation averaging out 2 packets of wet food per day.
Then you need to factor in the costs of annual boosters jabs, flea and worming treatments. If young cats, the first year you'll also have the first vaccinations plus neutering/spaying costs. Also the microchip for each.
Toys are cheap and tbh all my cats have preferred cardboard boxes, rolled up foil, bits of string so you don't need to go to town on those.
1 cat bed per cat - the doughnuts or igloos/pyramids are good. Alternatively use a cardboard box or laundry basket (the sort you carry) with a blanket in.
Until they are house trained or you let them outside they will need a litter tray each with litter. Again doesn't need to be expensive.
Collars don't need to be expensive, especially as many cats hate them and take them off, so just get a cheap reflective one each. Make sure they have a piece of elastic to the cat can free themselves if they get caught on something.