The vet behaviourist. Dr Ian Dunbar, has some good info on selecting a puppy on his website
http://www.dogstardaily.com/training/how-select-good-puppy. He also has other excellent (free) resources including the books
Before you get your puppy and
After you get your puppy. You'll need a free login to access the material but it's well worth it.
Couple of things to look out for. The puppy should be okay with people. Generally you want the one that looks confident (ie doesn't hide) but not boisterous. You're trying to avoid two problem traits - shyness and fun-barkers. It doesn't always work but it's a good start (my female was a hider but actually adores people - I got her for dog sports tho). Make noise around the pups and see their reactions. While it might be cute you may want to avoid the one that thinks the noise is fun (Shelties like to bark at things for fun).
I'm not sure you can select for a non-barker (except go for a different breed). My female came from a family of barkers, my male didn't, but he's a barker and she isn't. Shelties are more likely to bark in multiples so don't be tempted to walk out with more than one pup!
And remember everything you laugh at as a puppy can be darn annoying as an adult. Shelties are clowns and pleasers, so if they get a laugh out of you they'll keep doing it for life. There are just some things that Sheltie pups need no encouragement to do, like barking at plastic bags, electrical things, attacking the broom or rake - don't laugh at them when they do it. I learnt this the hard way and sweeping has never been the same since.
As for cats, I've always had cats and shelties and its never been an issue. Shelties are quite gentle and I don't think you could get a better breed for cats. I think the only issue would be a high drive sheltie may get over-stimulated when the cats play and bark at them.
If in the end you are tossing up between a male and female I'd recommend a male. I've seen more high drive females than males and it sounds like you want one a little laid back.