Wait, if you can modify skill interface..
That means you can remove skill lines and have an actual good GUI
*Runs out of the thread*
About the crossbows.. Why the hell not ?
Crossbows were used for that very reason : it was easy to learn, even for the peasants. But to avoid making it the simplest weapon to learn, and still an all-round powerful one, you should make very heavy armors like full plate and heavy scale very very strong against it