Grow your own trees! Automate wood production or grow your own forests.
Mods introducing new content into the game.
Furnaces, assembling machines, production chains.
I like the concept of choosing the tree type you want to grow.
(Several Factorio Mod Authors also do their own sprite art; perhaps a request to one of them for assistance... it wouldn't hurt to ask.)
Glad you like it! :D
I think I can do some decent-ish art for the mulcher, I just haven't had time. I quite like making art in factorio's style because it's sort of a hybrid between pixel art and realistic art. Thanks for the advice though :)