You will be able to put a 100 amp fuse on the charging side ,
( 90 amp Alt ) but the starting side is capable of drawing
400+ amps . No one I know of makes a reliable fuse that is
rated for that many amps @ 14.5v . I have seen people use
bar type AC fuses , but they are large and usually rated @ 220v .
so they react too slowly in a low voltage circuit .
Your other option is to split out the starter circuit at the battery and use
a starter solenoid close to the battery . This way the starter circuit
is open ( Dead ) when it's not in use .
It isn't complex wiring , but it needs to be done correctly because
of the amperage involved . That means quality connections and
carefully routed and protected cabling . If your not 100% confident
in your ability , then have it done professionally .