1.It is true that cats know their owners. They will remain faithful if they r happy & it does not take much to make a cat happy. All u need to do is feed it well, show it love & attention, keep it healthy & it is home clean & give it some freedom to play outside.
There is a risk of the cat getting lost but if u micro chip it, there is every chance it will be safely returned home.
Cats do sometimes fight (some more then others) this seems to happen less if the cat is spayed or neutered. If u get pet insurance, u wo not have to worry about big vet bills.
2. To stop cats scratching, there is a spray u can buy from vets surgeries but there is no guarantee that it will work. If the scratching would bother u I suggest u do not get a cat because they like to climb curtains, scratch wall paper, carpets, furniture, EVERYTHING!
3. It is most likely that the cat would want to attack ur hamster because it is their nature. Please under no circumstances put a cat near ur hamster. As for the rabbit, I also doubt they would get on. Rabbits r strong & either the cat or the rabbit could get hurt.
Cats r wonderful pets & I have had atleast 3 at a time through my life. They r fun, loving & great company but it does come at a price.
Please think about the harder parts of having a cat before u make up ur mind.
Be aware that they cost alot of money! You would have to buy a bed, litter tray & litter, food & water bowls, a collar, toys & food. Also they need to be wormed & de-flead monthly. They can easily get ear mites (it just cost me £40 to sort out my kittens mites). They need vaccinating yearly, micro chipping, spaying/neutering & they can injure themselves at anytime. So only have a cat if it is no problem to pay all of this.
I hope I have not put u off, I just want u to be totally confident with ur decision. Like I said, cats r amazing. Every single one I've ever looked after has had their own unique personality. They have all been a part of our family. Just be sure that u can give the cat a great life before u get one.
If u do get one, I'd advise going to a rescue centre for an older cat. That way, u can ask for one that does not seem to scratch. Older cats r much easier. Plus u would be giving an old cat somewhere to finally settle & be happy.
Good luck with ur decision.