I'm glad to see someone else tinkering around with these cells.
The temperature I saw was during charge and discharge. It stayed pretty constant.
IMO you really need a BMS unless you plan to babysit the heck out of your pack. I did this for a while with my Prius' PHEV kit and it gets to be a real pain.
I'm actually almost done
designing a BMS for my Prius' PHEV kit. It uses an Arduino and celllog8 devices for voltage monitoring. However, my next version of the BMS will likely be switching to the TI or similar chip to reduce cost and increase flexibility. It would also allow you to reuse that charger assuming you can adjust the voltage for the lithium cells.