Thank you to everyone who mentioned this - I've done it now and added it to the original post
They're all unlocked, the Mini-Me players literally start with level 1 across all stats, and they then gain XP by completing the skilling tasks. They level up exactly like a real player
I've taken this on-board and the Mini-Me's are now.. Mini!
Added to original post
If the player spends the time levelling up their Mini-Me, they can send them on tasks such as mining ores or smithing armour etc.
The player can then trade the Mini-Me and collect the resources at the end of the task