First, find the BIG fusible link. Follow the battery positive toward the fuse box until you find it. Check it's condition first. Once it is okay, start chasing down individual circuits and testing/fixing them as required.
The power at the starter is fine it has its own power cable, the main feed to the fuse box will have a fuseable link in line (usualy under 3 or 4 meters of tape and where there is no movement and something that will rip the skin off your kuckles)

some you can see if they are blown because they cause bubbles in the insulation others you need to put a meter on either side.
for all the accessories to have no power it will be in this main feed and if you follow that feed you will find it if you cant you can work out where it is by getting a needle and pushing it through the insulation into the feed wire and connecting 12V to the needle and seeing if you get 12v inside, and work forward from the battery until you get 12v (go half the cable then half in the direction you need (toward the battery if the needle gave you power toward the fuse box if it didn't) this will locate the link.
Legal disclaimer: Any information I may have provided is worth exactly what you paid me for it.