Larry Fishel wrote:
....

I will have 3 1/2" of space I can insulate in the walls and more in
the ceiling. Is 3 1/2" fiberglass insulation (R-13) the best I can do
here?

No. Likely the best you can do without adding thickness to the walls is
to use a foamed in place foam. Call around and find a contractor. The
stuff is not all that cheap, but it should not be too expensive for your
application and it will add quite a bit over what you have planed.

You may also want to consider adding a layer of rigid foam under the
outside or inside siding if this is possible with your construction. An
added inch or even less of high R value material will make a big difference
overall. This could be in addition to the foam in the wall cavity.

--
Joseph Meehan

Dia duit