+1 to what CB said...
If you're planning on down-sizing, converting as much of your lighting to LED will help on the battery. A modern Reg/Rec is a nice change, but not required. Can help with a smaller battery.
If you re-wire, do yourself a favor and interrupt the headlight circuit when the electric start is used. It will help alleviate any deep draw on the battery during the start phase. Understand the bike's electrical system first before you start down sizing. Else, you could be struggling to keep a battery alive.
These bikes operate in a draw state in the lower RPMs, so if milling and idling about is part of your riding environment, a full size (A/Hr) battery is important. The Shorai offers a 14 A/Hr small format battery in their A2 frame. Still very small, but $150.