Here is just my opinion of the cars that I have wired. Do not pull power from your starter. I run a minimum 4ga wire from the output side of my main cut off switch to a terminal block. There are blocks you can get from marine sources that have a large stud for the 4ga wire, then have smaller screws to send power out to wherever you would like. I use relays on everything, but definitely on large load items, so power can be pulled from the large + terminal block to them.
I also run a large ground terminal block with just as large ground wire coming from the battery to the block. To many people run large + wire but then use the chassis as their only grounding source. This can cause unseen problems such as water pump running slower than it otherwise could, etc....
If you use a one wire alternator get the main power switch that has the separate terminals for your alternator wire, that way it won't back feed and not let your engine shut down when the power switch is turned off.
There are really nice wiring kits that you can buy such as from K&R, but with a little thought and time a guy can do a really nice job himself.
Curtis