Wiring guidance for anyone adding components to their cars

[Steveyg777]

I created this in the hope that a sort of "wiring 101" guide could be on hand to everyone including noobs like myself. So please ask basic worrying questions here and then i can consolidate the guidance at the top after a while.

 

I've got since questions to start off with:

 

1. If i have multiple components to setup in the car can i connect them all to the same power line or should they be connected to different power wires that take power from different power sources (fuse box, directly from battery, etc)?
2. Can i take power from a fuse on the fuse box or should it be directly from the battery?
3. When taking power from a source should i also connect a fuse to the line first? And should it be the same fuse as the line output or the power draw from the component? (Hard wiring usb components that have a step down transformer from 12v to 5v for example)
4. What are relays and should i be using them or how do i know if my scenario requires one or not?
5. Are particular wire connecting devices recommended (list some links to good ones please) or should i just splice and twist new wires to one another then cover in electrical tape?
6. Is there a rough limit on how many components i add to my car, or, how do i know when i need to connect a second battery to the power system to balance the load?

 

There may be more questions, or concerns that arise but answering these works really help me figure things out for now.

[Ootohere]

@Breezy_Petemight be someone that can assist.