The brakes and derailers should work fine, all you're going to need is a new cockpit.
Just about any mountain bike lever that's marketed for use with cantilever brakes will work.
As far as shifters goes, you don't have many options. You can either go with the Thumbies you mentioned, which are beautiful, but not cheap, or you can use a pair of the ubiquitous
Falcon thumb shifters, which are cheap, but in no way beautiful.
You could try and track down a used pair of Suntour Power Ratchet thumb shifters, which would be my preference, they show up on ebay quite often, are usually reasonably priced, and work beautifully.
You can also find the appropriate indexing lever for your cassette, which would be moderately priced, but slightly less versatile.