dw expanded canon

I’ve been playing Doctor Who Legacy like a maniac today in my mum’s phone, and it is suuuper fun (like worlds in time was before they ruinned it 5ever) but lol I really wish they had a propper set of FAQs for the mechanics because there are a few things I still don’t get, like:

a) Once a companion is “leveled up” to the max, is there no way to give them higher stats? because I want to keep using Sarah Jane but it says she can’t level up any more…

b) How exactly are the crystals “dropped”? does it need to be exclusively for new missions, or could I just go to an earlier one and farm them? or are they fixed by levels?