No scar I learned to fly on a grass strip with an Eaglet 50 powered by an OS FP-25 Never have used a paved runnway
Also flew several Royal 20T and 20S with the same engine all from grass strips.
When flying off grass I simply increase the size of the wheels I believe I was using 2.50" nose wheel and 2.75" mains but I may have gone as high as 2.75" nose and 3.0" mains.

Just so you realize this most of my recomandations are based on actually having done it not just idle speculation Sorry I wasn't more specific.

P.S. .25 sized planes are easy to hand launch also... Guess how I Know

I almost forgot I've got a modeltech .25 J-3 Cub that has no problems taking off from a grass strip with an FP-.25