any time you connect to a battery you want a fuse (or breaker) as close to the connection as possible. An inline fuse holder works great. Your main fuse that supplies power to your fuse panel needs to be rated to support a little more than the sum of all the devices you will use. The helix 7 says use a 3 amp fuse, the actual draw of the 7 is probably 1.5-2 amps and will say in the specs for the device. You get the main fuse size by adding the actual draw.
Ultimately the fuses are only to protect the wire from becoming hot knives and catching fire when something shorts out.
If it was me I would get a blade style fuse panel on amazon and put a 25amp main fuse at the battery and a bunch of 10-15's in the panel for your devices. You can always use a little bigger fuse, but you cant go smaller. If your device itself fails having a perfectly rated fuse is extremely unlikely to save the device as a fuse pops because the device already failed. Dont let people scare you, this isnt rocket science but you alway always ALWAYs want to use fuses. Even a single fuse at the battery would be sufficient for safety, but if one device or wire fails all your devices would go out which is why you break them down with individual fuses.