Prusa2 build Questions RAMPS/Power/Wire/Thichsheet

Hello Reprap forum goers, I have slowly been building my Prusa2 for awhile and I have gotten to a place where I need advice.
As background, I did electronics in high school but building this reprap is my refresher course (boy do I need one!)

1. As far as the electronics go, I have a RAMPS 1.4 and Mega combo. To load the firmware onto the mega I will have everything disconnected from the board (including the RAMPS board.) Is this the best practice? can you put everything together and then update firmware, software as you please?

2. Power. I decided to modify a ATX PSU and successfully harnessed up all of the live wires and grounds to binding posts. My question is, if I run 2 pairs of wires that connect at the ground and 12v posts to both the 11A and 5A draw, will I fry anything (in my head the 5A for the electronics would never get the full amperage because it draws on other wires, just not sure though.) Alternatively could you have the wire split farther up the wires like a Y? (I have banana connectors that can take 15A that I want to make the wiring harness out of, bad idea / good idea?)

(Sometimes I wish I had not used the binding posts and just used the wires already there. Oh well)

3. Do you have to use high temperature wire from the hotend? it seems like some people don't.

4. I decided to laser cut a single thick sheet for my build as I have a MK2 heated bed. In the picture I have the bar clamps "upside down" is there any problem with doing that? The only thing is it affects the build area but it gets the bed high enough that it doesn't hit the belt guides.

Thanks so much for your time, see the attached picture for some of my build, including my electronics mount for the side with Escher birds.

1. You can upload the firmware with everything connected
2. You can run separate or split the wires from the PSU to the two inputs as long as the wire will take the current. The only thing to watch for on ATX conversions is whether it maintains it's voltage under load, some PSU's require a load on the 5V line in order to output a consistent 12V under load.
3. The wire needs to be a decent size so it's not a significant part of the resistance in the circuit, but the heated bed doesn't get that hot, I run 18Ga wire to mine, I like Nopheads idea of running ribbon cable to it and using multiple conductors.

Thanks for answering my questions!

So for the splitter I could run 12awg for the heatbed to the ramps and splice in 18awg for the electronics 5amp in to one set of banana connectors and I would be ok?

I just discovered I may have to connect the hotend resistor to the wire using crimped connections? because the solder might melt? has that been your experience? (makes sense due to the temperature.)