Here is a list I put together when I started planning the electrical to get an idea of placement and load so I could plan circuits etc. Of course what goes along with that is the layout: How far apart are electrical components. What other mechanical systems will be competing for space.
Don't forget about any electrical connected to any plumbing in the belly pan: tank sensors, pumps.
Regarding the 7 wire cabling for lights and brakes will you be going with magnetic drum or electric over hydraulic brakes. If EOH I would recommend going with the larger gauge cable like this.
It has heavier gauge wire for the power, ground and brake circuits.
Batteries, inverter/charger can be a more complex solution.
What is your goal - always in RV parks with power available, boon docking.
If boon docking and you want AC, start thinking about a generator.
What type of load will you be using when not on city power and for how long.
Solar - how many - mounted or portable
Is your end goal require more capacity than you will start with. If so, will you size components for the end goal now or replace as capacity increases.
A lot to plan and sort out. You can get there just start planning and ask lots of questions.