first time wiring a new system

As the amp is not internally fused, use your fused distro block within 18" of the amplifier if possible. This fuse is designed to protect the amp unlike the fuse at the battery which is designed to protect the vehicle.

Still stand by the no cap necessary at this time. A cap does not make power, it stores and uses it. If your lights are flickering, the first thing to do is upgrade all wiring at the battery / alternator, next upgrade to a better battery and next if it still not good enough is to add a HO alternator.

Rob- Based on what you said, I doubt I'll need a cap or likely anything else for awhile.  I will be using the xtant 403a amp to power some cdt door components and one re-10 sub( sub at 200w rms @2 ohms). The amp/crossovers will be under the driver's seat and the sub box will be under the passenger's seat. Based on how close everything is to each other I should be able to get that f.d.b. within 3-4 inches of the amp. 

Are there any consequences for mounting the amp/f.d.b that close to each other?

 I hope this relatively low wattage (@3-400w) will not affect the lights or anything, but I guess I'll find out what I'm in for when/if I ever add another amp so components/sub can recieve seperate power.