Think about what the end result is that you are looking for and start with that finish. Mixing and matching has it's place, but most finishes are designed to stand alone. I think if you try to do CA over oil, you may end up with issues getting them to adhere to one another.

Oil finishes bring out the luster and depth of certain woods. Some wood dont' really benefit from them. If you have a lovely walnut burl, the oil will be a perfect choice. if it is a non-descript wood, you will spend lots of time maintaining the oil finish when you could have put on a shellac, varnish or CA that would hold up much better.

I love oil finishes (i'm a woodworker, BTW) but I don't use them on scales because of durability issues.

Goog