I use the small fuse block as well. I have a main fuse rated for max current at the battery. Then each line coming off the fuse block has unit recommended fuse size. The fuse block is easily accessible at the console, and i removed the fuse coming off the sonar. Those cables are buried under the front deck, and not easily accessible. I have a led switch for each unit on the front deck panel which easily allows me to see if power is at the switch if it's on. You will be surprised at how much current all the units can pull together, and a battery current calculation will tell you how long you will run before you will run a battery down too low. I would setup a low battery voltage on your units so you don't take a certain type of battery down too low. Some types (wet/agm) don't like to go down below 11.2vdc, it is harder on the battery life. Note: I run electronics on a separate battery so I don't run the starting battery down too low. A 55ah battery lasts @ 8 hours with just the 1222 garmin/livescope. Running helix 12 side by side with the garmin uses some juice. I have plenty of batteries, but changing up setup soon with lithium. It not that complicated, but doing the wiring can take up some time. Don't use butt connectors, solder and shrink wrap wiring for everything. I use powerpole connectors on everything, so i can swap batteries in seconds if needed.
Here is a link to see how your battery will do if you know the current values
Battery calculator