Hello!
American Autowire (pn# 510662) makes a complete wiring loom for our cars ment for a aftermarket build with circuits for a one wire alternator (which isn't for everyone... but it does work, they are on a gazillion hot rods), fuel injection, electric fans, digital dash etc....
It comes with modern blade fuses and a bunch of connectors and switches and of course instructions. This, obviously is a big job. I ordered a kit myself and am very impressed with the quality so far, however I haven't installed it. It is pricey but so far it seems worth the buck.
Link
https://www.americanautowire.com/shop/1971-1973-ford-mustang-classic-update-kit
I also have the Dakota digital dash. They have a lifetime warranty on all their stuff. They make a quality product as well.
I have this model. It can do so much more than just be a gauge.... speedometer sensors (manual gear type and electric with a fairly easy calibration setup), control electric fans, give alarms at overtemp or low oil pressure at a temp/psi of your choice, etc.... again.... in my opinion worth the coin. I went with the VHX with the 3 gauge style
Link
https://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=922/mode=prod/prd922.htmAs for the 3 gauges in the center console, I bored out the holes with a file (just slightly) and put a oil temp gauge, air fuel ratio gauge and ambient air temp gauge in the holes. Just find 3 gauges that you like that are 2 1/16 in size and bore out the holes alittle in the center console and they fit right in.
I am running FITECH fuel injection because they use OEM parts (injectors, sensors etc... so replacements can be bought at an autoparts store) in their setup and the classic model looks like a holley carb. I went with this because the computer is mounted in the car away from heat and I think it looks cool. Good for 650 horsepower
Link
https://fitechefi.com/product/30021-go-efi-classic-black-650hp-system-2/I have used their stuff before and, for me, it works great.
Aeromotive makes a bolt in tank with a electric fuel pump in it (stealth). That fit well too, ment for fuel injection with everything in factory locations.
I put the battery in the trunk as I plan on autocross driving the car because I have a screw loose in my head.
Mike Maier makes some awesome subframe connectors and suspension components for our cars. Fit up is perfect and quality is top notch.
https://mikemaierinc.com/
Anything is doable, as others gave stated, Google is your friend here because your questions aren't specific enough and cover a wide range of topics that lead down so many rabbit holes. Basically my advice is.... find parts you like and WILL them on your car. The parts I mentioned work nicely with our cars. I haven't ran the battery cables yet, BUT I HAVE POWER TOOLS!... so I'll figure that out when the wiring comes.
As far as the debate if it is worth it.... it's not about the weight transfer ratio (ie moving 20 lbs from front to rear isn't that much weight compared to the rest of the car) as it is about the effect of not having that much weight hanging in front of your front tire over the nose of your car. Street driving only.... I'd personally leave it up front.... simply for convenience. Performance build for spirited driving and occasional track days... move it.
Attack the car.
ENJOY THE PROCESS! Don't rush it.
-Manny