My god – so much advise – some good, some crap (as to be expected on here 😉 )
ime, they're certainly loyal little dogs and good guard dogs but they genuinely can be snappy little buggers; down right aggressive in some cases. A lot of this comes down to training/husbandry, some is down to breeding – definitely worth taking advice re breeders…stay well away from the "farms" so infamous in SW Wales but rife in other areas too.
Main health problems are Skin, Skin, Skin and Skin. They're by far the most prone breed to various allergic skin diseases, most requiring life long medication to keep the dog comfortable. I'd ALWAYS recommend getting good (life long) insurance if you get one. There are good treatment alternatives to steroids if you're unlucky (none of the potentially nasty side effects) but they are silly expensive.
As for having one in a one bedroom flat – as long as they're not left alone for too long at a time and they get regular exercise I don't see a problem. Just go see your local vet after purchasing – many will do cut price post-purchase health checks and give you loads of good advice, especially if you start their vaccinations at the same time.