From what I understand, soldering LiFePO4 batteries will make you sad. Spot welding your nickel tabs is what you really want to do. My batteries (which are totally wrong for ebike use, but I got them cheap... $7/cell and I'm just doing 1P) are screw terminaled with solid bus bars and heavy duty interlocking plastic holders.
They look just like this:
https://www.copybook.com/companies/goodwolfe-energy
What motor are you looking at? I recently got a Bafang BBS02 mid drive. The kit is very complete and the only thing you really need to supply yourself is the battery+bms.
As for BMS, the best one for LiFePO4 is the SignalLab (now Ping Battery). That's what I've bought. I did my initial chargeup and everything is going well. I just need to wrap/mount my battery now:
What's new on V5 LiFePO4 BMS (Battery Management System)? - PingBattery