Various things:
If you have a savings buffer, and could fork out 10k for treatment (vet bills can rack up very quickly), don't bother with insurance. We've had dogs for >20 years, usually two at a time, and though we've had to pay for the odd operation etc, we have saved a fortune (about 15-18k, I reckon, though that is very back of the envelope). By the time the dog is almost guaranteed to be needing treatment for something (arthritis etc) your premiums will be through the roof anyway. It's a personal decision, and partly depends on how much you'd be prepared to pay, or put your dog through, to keep it alive. The point where I think it's no longer fair to the dog to continue with treatment might be well before yours.
Cocker spaniels - be very aware that there are two very distinct groups of cockers, the very fluffy long-eared show-type ones you'll see on the Crufts coverage in the next few days, and the leaner, less furry working variety. Obviously you'll get the odd show cocker that has mad prey drive and lots of ambition, and the odd working cocker that hasn't any of either, but on the whole, working cockers are a very different deal. We see a lot of people on this board who have a working cocker that they adore, but which is resource guarding the sofa, biting the DC, has no recall, can't be walked in the evening in the winter because car lights send it bonkers, whatever. This is not because the dog is fatally flawed. It's because the dog is in a home that doesn't give it an outlet for its genetic drives. It might have puzzle toys and do 20 mins a day of 'working on loose-lead walking', but it's not getting the chance to hunt and find and retrieve that it's been bred for. You don't have to take the dog on a shoot, but you do have to instil a stellar recall and then provide a facsimile of gundog work if you want it to be happy and fulfilled - hide tennis balls in long grass, send it back 50 yards for something you've dropped, give it the chance to have a damn good sniff and explore around a rabbit warren. Not every working-line cocker needs this, but quite a lot of them do. (I have working-line dogs of another breed and they are SO much nicer, and easier to handle and live with, if they get what they need.)
Rescue dogs. Be very cautious which organisation you go to. Spaniel Aid and English Springer Spaniel Welfare (who get a lot of cockers despite their name) both have a good reputation and do seem to understand the dogs they have in for rehoming, They're fostered, so the fosterer is able to see what the dog is like in a home, out on daily walk, with other dogs, etc.
Grooming. Apart from getting a coat full off burrs etc, intact working cockers don't seem to need a lot of grooming beyond the odd brush (I can't speak for show lines, but given the hair...). Neuter a spaniel, and the coat is likely to go all cottony and weird (I've seen this with a friend's springer). Cottony coats are liable to matt.
All that being said, I love having dogs. I was out with mine for >an hour this morning, mostly letting them free run, though we did a little bit of basic training. The sun was shining, the skylarks were singing, the blackthorn was coming into flower - but even if it's half dark and cold and the rain is horizontal, I still like taking the dogs out, because their enjoyment is infectious.