I have several persian cats, and although i too have also heard about their poor toileting behaviour, i can honestly say my cats are very clean and have never had toileting problems.
However i do keep all the litter trays very clean, i scoop them out twice a day at least. In fact i have found that even if the cats have an upset stomach they still always manage to make it to the tray, unlike a DSH and a ragdoll i used to own.
As for them getting along, it really depends on the individual cat. Persians are extremely laid back, complete lounge lizards, with only the occasional active ouburst. I know that Ragdolls are also meant to be quite laid back, so with the correct introductions i don't forsee any problems.
I do still think though that some cats will want to be solitary, and no amount of trying will get them to 'like' other cats. I brought a persian once who was absolutely lovely with people, extremely affectionate etc, but HATED other cats. No matter what age/sex, if a cat was within a metre of it he would lash out. Unfortunately things got so bad he had to be rehomed with a freind, where he is a single cat and is absolutely loving it.
However i must admit, i should have picked up on the warning signs ie when he was with his littermates or mum, he'd growl or hiss at anyone who went near his food or him. So choose carefully. Find a good breeder, whose cats are friendly and all should go well