Learning about batteries

We have taken the decision to get the 48V 1000W motor, so now, we need a 48V battery pack.
There are several options, between 10Ah and 20Ah, and two main technologies:

• LiMn2O4 (Lithium Ion Manganese Oxide): 3,7V cell. Recommended for up to 15Ah.
• LiFePO4 (Lithium Iron Phosphate): More expensive. Recommended for more than 15Ah. Flat discharge curve. 3,2V cell.

We have decided to take the big one (LiFePO4 48V 20Ah), so that if we add a second motor (front wheel), we don't need a second battery pack.