Hi! We have a Cavalier King Charles Spaniel, fantastic family dogs!
Can't give you much in the way of advice on indoor potty training as we didn't do that. We did get those pads for the first winter as the snow was about three times deeper than his height and he did well with that. Switching him to the outside in the spring, well... that was a pain.
Grooming is something that should be done pretty frequently or you might run into problems. They have a very fine undercoat that tends to mat pretty easily, mostly around their ears. They're a true lapdog, so I just sit and comb him while I'm watching tv every night, once a week he gets a "good" brush and comb out. I also need to trim up the hair that grows on his feet and in between his foot pads occasionally.
As for price, $400 seems quite low, be careful of that. I can't remember exactly how much we paid for Quincy, but I'm sure it was more than that (CAN) and he's CKC registered but pet quality. There's the runt of the litter, then there's Quincy. He's big boned, so a little on the large side to be a show dog.