You can use door caseing of any width. Just rip it to fit at corners where the space is narrower than the board. See this video for "how to".

Can a colonial baseboard look okay with a craftsman flat casing? (Doors are raised 2 panel square top).

It looks fine if you think it does. Its a personal choice. I would not do it, but that's my personal choice.

Can a craftsman style flat baseboard w/flat casing look okay with a traditional crown molding?

Sure. Done all the time.

Wainscoting - Can both a craftsman style wainscoting and pencil frame molding wainscoting be used in different rooms in a house?

Yes.

Good luck with the project.

@StarCraft Custom Builders Thank you! After watching the video, I'm assuming using flat casing vs. colonial style would look better since there are no lines to match up after cutting the one side to fit.

We opened up a wall between the dining room and kitchen and I'm planning on having crown molding put above the kitchen cabinets. Since the rooms look into each other is it best to keep the kitchen crown molding the same as what is already in the dining room?

I like the cleaner look of the flat base/casing with my new doors but don't want it too contemporary or too trendy. Seems like much of the newer homes and remodels are using the craftsman trim as it blends with lots of styles. Here's my doors.