Feliway plug in diffusers are an excellent product. I have found them at an online store for a good price. I'm not sure of the rules here for posting those kind of links, if you want more info feel free to PM me. Yes it is available in the USA. I use it.

You should also get a black light to be sure all soiling has been removed. Just because you can't smell it doesn't mean he can't. A black light will show you any spots that odor remains in.

It sounds like you have enough litter boxes. Three for two cats should be enough, make sure they are kept spotlessly clean, some cats really hate to pee in dirty boxes. Make sure the other cat is not barring him from using them. This can be done by keeping at least one box in a different place than the other two.

You said he's been to the vet, but did not say whether a urinalysis was done. If not, I recommend you bring him back and get that done. The only way to know what's going on in the bladder and urinary tract is for urine to be taken and tested (best to be sent to a lab)

As for the other stuff, the chewing and counters and tearing things up, that is normal behavior for a year old cat, especially one with too much energy. He needs interactive play, one on one time with you, or another human every day. Interactive play with string on a stick toys, or throwing chasing catching games, that get him your attention and get him running and leaping.

Give him a cardboard box, with the sides about 4 inches high, with the flaps torn off for his own chewing pleasure, and keep things off the floor that you don't want chewed, or that he might be tempted to pee on.

Cats like to jump and climb and to be on high things so he needs a cat tree of some sort, or a couple of graduated high bookcases, with the tops cleared for him to climb and jump on. If he has his own furniture he will be less likely to jump on things you don't want him on. You can help him understand that by, when you catch him on the counter, take him over to his own perch.

here is an example of what I mean about the bookcases