Assuming that you use a manual fuel pump, a rechargeable glow driver, and hand start the plane as you say, then you don't need a power panel.
However, there might be a time when your engine won't co-operate, or your glow starter has gone flat and you don't have a means of quickly recharging it.
When I got my box, I chose the GP Master Caddy which has a detachable power section which holds the battery, panel, and has a shelf for the starter. I got the full kit n' kaboodle at the time: a battery, panel, starter and electric pump. I already had a rechargable glow driver so I don't use the 1.2v output for that but I do have a wired glow lead as a backup. I also have a muanual pump which I now use more than the electric.
It's really a matter of convenience against familiarity with your equipment. My first engine would not co-operate and it would take ages to start manually so I felt I needed the starter. Now I have engines that will start on the first flip...