It sounds overly complicated to me. I understand your wanting to go lightest, but remember lithium ion cells have a shorter life, you loose 10-20% per year capacity so you have to figure in replacement costs. Also inverters are inefficient unless you have a really complex and expensive design so your going to be wasting a lot of energy there and your not going to run much of anything at all off of a handful of small cells like that (remember power in = power out so when you jump the output voltage up 10x you pull 10x more current on the input.)
As someone else stated, a 12v sla and some fuses and connectors will give a simpeler solution.