For a safe installation, you need a fuse as close to the battery as possible.
You should also fuse any lines where there is a change in wire size, which usually means after a distro block.
As far as the fuse sizes you need, we can't tell you without knowing the total amperage the equipment will draw.
There are tons of guides to choosing proper fuse ratings on the web. I'm pretty certain there's one on these forums, as well.
Now tell us about your carPC....