If you want to run both, you'll have to isolate them with a switch so your either running the AGM's or LFP but not both. Then you have to consider the charging aspect and even with BB's you still have to be within a certain spec for them, a 2 stage charging process.
Tesla Packs are not LFP and that is even more persnickety and their voltage range has to be adjusted for. DIY is likely the better option, you can make a 200 / 300 or even 400AH 12V pack. 200AH cells can be had for as low as 71 USD ea, 4 cells = 12V plus BMS & Shipping
Catl Lishen 3.2v Lifepo4 202ah Lithium Batteries 3.2v Lifepo4 200ah Battery For Ess,Off Grid,Home Solar Energy - Buy Catl,3.2v Lifepo4,200ah Lifepo4 Product on Alibaba.com
deligreen.en.alibaba.com
EDIT: Adding switch link
350 Amps continuous rating for inboard gasoline or diesel engines.
www.bluesea.com