Reddit reviews InstallGear 4/8/10 AWG Gauge Power Distribution Block 4 Gauge in to (4) 8/10 Gauge Out
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4 Gauge In to (4) 8/10 Gauge OutHigh Conductive FinishCrystal Clear CoverDurable High Temperature Base
First off, if this is all the electronics that you are planning on running you don't need a subpanel.
You should be able to get away with a 20 amp 120v receptacle. To be safe I'd run a 3 wire 12ga romex and run a 20amp receptacle with both plugs being on a different circuit. That way if you end up needing multiple power supplies you have the circuits for it.
The cheapest solution would be a computer power supply. They will be quite a bit cheaper than buying a legit 12v supply because they are a commodity item.
Easiest way to size it would be to tally up the fuse sizes in all the amplifiers and then multiply by that by the voltage (12) to find the required wattage.
You'll probably be fine with a 1000w power supply like this one:
https://www.amazon.com/Seasonic-Titanium-SSR-1000TR-Modular-Warranty/dp/B075M8FH4C/
If you read the specifications for this power supply you can see that it can output 83 amps on it's 12v rail. If the total draw of all the amps is under 83 amps then it can run them all.
Power Output
AC Input Voltage: 100 V - 240 V
Current: 11 - 5.5 A
Frequency: 50 Hz - 60 Hz
DC Output Rail +3.3 V +5 V +12 V -12 V +5 VSB
Maximum Power 25 A 25 A 83 A 0.5 A 3 A
125 W 996 W 6.0 W 15 W
Total continuous power 1000 W
Depending on how important reliability is you can buy a crappy chinese power supply but I'd recommend a decent brand name.
One thing with buying a computer power supply is that you need to make sure that you find one with a single 12v rail. That will make things a lot easier for you.
Once you have your power supply there's a ton of info on how to set it up to run your amplifiers. Here's one tutorial that I found: https://www.instructables.com/id/Car-Amplifier-and-Subwoofer-Powered-By-a-Computer-/
For your application I'd recommend a decent distribution block to make wiring easier
https://www.amazon.com/InstallGear-Gauge-Power-Distribution-Block/dp/B01DCDG9JC
And if it is at all possible I would highly recommend returning the 12v amplifiers and buying 120v ones. It will make your life a lot simpler.