Top one should be 15 amps. then 7 and 5 I think. If you have the fuse cover, it shows the order. At least my 78 does.
You can plug in an led taillight with no issues.
If you do signal lights though, you either need a ballast(waste of power) or an electronic flasher for about $10.
The ride IS the adventure. The destination is just to get gas!