The leather is sturdy and will be durable. Easily scuffed but the more battered these things look, the better. It is easy to add extra inserts using spare elastics (but remember to buy these when you buy your notebook). Attaching charms is also pretty straightforward. The nice thing about this system is that there is no right or wrong way to do it. All that matters is that it works for you.
Basic instructions come with the notebooks but there is a plethora of videos out there to help. Take this one for example:
I got these from The Journal Shop – they have free shipping and parcels arrive blisteringly fast – door to door in three days for me.