Is that the result of blisters? Or are you referring to the minor damage at the bow? Unless there's a lot of core damage that doesn't look that bad. Not even sure that there's any core in that area. It's probably the strongest part of the boat.
Really depends where you locate the battery. You want it as low as possible and well secured. For racing we use the smallest battery that we can get by with. Thus our conductors are 12ga. This calculator will help. Cable Sizing Calculator - myElectrical.com
Used Boat Buyer’s Guide | International J/24 Class Association
In 1980, Tillotson-Pearson, Inc. (T.P.I.) implemented two major construction changes on J/24s. The new style hatches appeared and vermiculite was removed from the sumps. This occurred at roughly hull #1900. If at all possible...
One of our crew has one on a Catalina 22, which is not a slippery boat. Works fine for getting off the dock and a few miles home when the wind dies. The Cat 22 ain't much of a drifter. You may want to check out the Elco electrics too.
Yes you can sail the 24 with the mail alone. I've rigged my 22 for single handed sailing with the main and blade. This fine for light going during evening races. When the wind builds you'll want some crew weight.