I have come across an airplane not knowing what size engine to put in it. It is called a "Soft Touch" 90 inch wing, 1425 in wing area, high wing. It is a very strong stuture. The plane weights 12.5 lbs empty. I have seen these engines for sale, used, relatively inexpensive. Am I even close to the right size engine?
MDS 2.18
magnum 1.8
Supertiger 2350
Any input is better than what I know about the big birds.

You are probably pretty close. Of course it depends how much wing area you have and how you plan to fly it. You could probably even use a 120 although it might not have as much power as you would like. If you aren't too concerned with performance and want to go cheap(relatively speaking) you might consider getting a reasonably priced gas engine such as a Ryobi 31, US 35,41 etc. Then you will save even more on fuel.