First startup attempt, Melted wire....Help!

It may be impossible to answer your question because the wiring MAY NOT BE factory colors. Example, why is there a blue connected to the starter relay?

A fried wire that large ALWAYS indicates a bad short.

HOW TO CHECK FOR SHORTS without burning up more "stuff."
Get yourself some large wattage 12V lamps as well as a smaller test lamp, test LAMP, not an LED

Disconnect the battery ground, and wire a BIG 12V lamp in series with the ground wire to the battery. The lamp will light if there is a big short. A headlamp works well. For "a smaller" load, use an old tail lamp socket with a 12V stop and tail lamp in. Go around pulling fuses and disconnecting until the lamp goes dark.

ALSO do not forget to disconnect such things as the alternator to check for shorts. The alternater may example, have a shorted diode.