So the motor from the mojave is 2100kv vs the 3200kv blx100 system. If you plan on 4s I would start at 20t and see how it goes. I currently run my BRCC with the 2100kv motor on 4s 20t and it runs great. Is it faster....no.....probably around the same as the blx100 stock. What is the goal of putting the 6s system in a 3s rig. Are you looking for speed runs or bash?
The 150amp esc is a tough fit in the same spot. You can do it with zip ties and/or servo tape. You might want to look at the 120 or 130amp as it runs 4s and bolts into the same holes as the blx100.