Chihuahua Grooming Question

If there's anyone here who doesn't know we have a new Chi pup then you must have been hiding under a rock for the last 2 months!!

Petey is a long haired Chi and is pretty good about being groomed. His coat is not in all the way since he's only about 4 months now. I'm wondering what is the best type of brush to use for his coat? Or should I use a comb?

Before we brought him home I picked up a tiny little slicker brush for him...but it's too harsh for him I think. I've used it on him, but I have to be very careful and gentle so I don't scratch his skin...and he really doesn't enjoy it.

I've looked things up online and all I keep finding is suggestions to use a "soft bristle brush". Two problems I foresee with that...1) Where will I ever find one small enough for my little 3 lb. Petey? Most of them are too big to use on our Sheltie. 2) How will a soft bristle brush really comb out the hair behind his ears...the longer hair that tends to get "crimped" looking about 3 days after a bath. I know once his coat really grows in he'll have the same type of fringe on his legs and tail too. I don't want him scruffy looking all the time...

My last question is how often to bathe him? I've read everything from once a month to once a week. My other dogs get done about once a month. I can't figure out what would be so special about the Chi coat that would be ok for it to get washed once a week...is there something I'm missing?

Thanks for any advice!
Heather & Petey