No rules of thumb. Just what looks best with your eye. I'm not a huge fan of knobs so I'll probably put pulls on everything. Many people do it.

Have you seen the Finished Kitchen Blog? You can scroll through pics there of dozens and dozens of finished kitchens and check out knob and/or pull placement and types. A google search will turn it up. I can't get the link easily right now.

You've got one decision made--the finish. Thats a good start!

I've seen all kinds of combinations. The only thing many people (and my cabinetmaker) agree on is that if a drawer is pretty wide -some people say more than 30" - it looks better to have either a much wider pull, or two pulls or two knobs. One knob or one small pull in the middle of a long drawer looks kind of out of proportion.

I have read that pulls can be practical, where you can loop just a wet or greasy pinky through to open instead of having to grasp a knob with dirty hands. My cabinetmaker pointed out, though, that the finish under the pull sometimes gets worn over time from fingernails scraping. I figure that's what scratch cover is for. The conclusion I've drawn from this discrepant info is what breezy said - pick whatever looks good to you.

Be sure to get samples. Things I thought looked good on line didn't work as well when I held them up IRL.

I am an advocate of all knobs. If you have good glides/hinges and a knob with a large enough head (not sure if there's a technical name for it!), you can use just a finger to open a door or drawer. My eye prefers knobs because I find they aren't as much of a focal point when I look at a kitchen as pulls sometimes are. Of course, it depends on the knobs/pulls/cabinets/etc.