I can help you with everything except the horns...I can't weld worth a shit but not next weekend..I'll be out of town. The following weekend is the get together and then Sunday is Easter. The following weekend I am open?
No silicone....It has a chemical in it that will eat away at the wire jacket. I use polyurathane sealant. Some use butyl rubber. I bought a white pvc fitting but did not like the way it fit. If I want to add more wire down the road, I will just poke a hole thru the sealant, its plyable like rubber.