Before you go adding a lot of complication to your electrical system, consider whether a battery with additional amp hours and/or CCA will serve your needs. It does seem odd to me that the addition of a couple aux fans and the blower fan onto the starting load would cause a no start condition. For comparison's sake, a stock size battery in my W124 has no trouble starting the car, even with the A/C running, 1500W of stereo turned on, and the air compressor for my air ride running. And that's on a diesel, which already has the very heavy draw from the glow plugs. I'd be wondering whether your existing battery is up to snuff.