Keep in mind that you will also have your upper range speaker amp(s) to account for the draw, aswell as little things like the HU. It also depends on the nominal load you are wired at.
It may bea bit over 200a when you add other amps into the mix like a 2, 4chan, both, etc. Say you are only using a 2chan amp that does 50wrms x 2...As inefficient as A/B amp's are, you can be drawing around 20 amps from that amp alone, and perhaps 5amps from the HU for a vague example.
You always want to be "safe" and power your equipment properly so you will want to over generalize the power you will be needing.
This dosn't however mean that you need a total battery Amp-hour, and alt figure of about the max Amp draw. It dosn't work this way. (both ratings aren't car audio ratings, however you can use them if you know how to)
Personally I have an oldschool xtant amp that does about 75wrms x2 at the load its at, and I also have a bc2k awell at 1 ohm. For Electrical I have an XSpower D3400 added as a secondary batt and upgraded power wire under the hood(big 3), stock alt. It works fine.
Amps do not constantly do their rated output anyway it varies on your subwoofer/ box. Some boxes may be more power hungry like small boxes for instance.