I have never seen a pneumatic one although that doesn't mean there aren't any. Electric would be cheaper and no air source needed. Electric is limited to about 1800 watts or 3 1/4 to 3 1/2 hp according to manufacturers specs. The more power, the harder to control.
No matter what size, you will be limited in depth of cut. Also, a router is not meant to be held freehand in midair. That's why they have a base on them. A dremel would be good for fine detail, but I think your primary weapon is still going to be the chainsaw. By the way, a full size Porter Cable router is as heavy as my old 98cc Stihl 066 without bar and chain.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.