MMMM... See your dilemma, well most spots further away from town are 14 day moorings. Closer to town the days get shorter. Biking into town even from the kidlington area is defiantly do-able, 5-6 miles? And as for leaving them, they are pretty safe,ive not heard of anyone having any trouble, There are always lots of people about to keep an eye out, leave your number with a few neighbours just in case. You can buy a winter mooring which is about £250 for i think between sept- march ish.
There are boats that come up with moorings but more pricey. An Agenda 21 Mooring, attached to a sale, is an extra £10,ooo and im fairly sure it can only be transfered once, but ill check on that. So always check its transferable with the seller first.
Moorings tend to go pretty fast here so act fast if you see one!
Hope thats a help.