Is it hard to learn how to create templates and a complete webpage?
depending on your skills, and learning capacity
Photoshop skill, and a little bit of HTML . nothing more lol. (also AfterEffects but that doesnt matter at Themeforest) Maybe is it can learned by like 2 years? or 3 maybe? I would like to try myself in this thing!
If you know AfterEffects i think you have more possibilities to make money (and far away less competence) on VideoHive. Considering the learning curve needed i guess you should think it twice. Just my 2 cents.