Besides typing your own words or trying the community ones? A lot of letters have multiple recipes, so I guess you could challenge yourself that way (if you haven't yet). Then I think it would just be minimizing everything you can, less factories, feeding multiple letters from the same machines, making it faster/more efficient, etc.
I would like to see lower-case added, we just need a way to make a dot I guess...but then numbers or non-English characters there's a lot of potential.