Just wanted to share this source for LiFePO4 batteries, as I wish I had seen this earlier:
The first option is a serious alternative to LiPo packs. Competitive in price, super easy to assemble, safe in operation and long-life.
The second option is pretty much identical in every aspect except chemistry to a 5p setup of 18650s (Samsung 30Q). But it will give you a longer lifetime and is easier to assemble (5x less cells, no need for welding).