It's worth pointing out, true, but I don't think in 99 percent of case this is realistically a problem. Meanwhile, there are several big advantages to USB based interfaces.

There are means of dealing with lots of USB peripherals.
First, if you have numerous USB dongles (or other low bandwidth peripherals), those can be placed on a USB hub.
 
What you don't want is your audio interface sharing a Root Hub with another higher bandwidth peripheral (HD or SSD).  As long as this isn't happening, your USB audio interface will be fine.

My only concern with the OP is that it seems to be an "all in" mindset, yet acknowledges the "steep learning curve" and "under utilization of Photoshop and Lightroom." First advice is to be realistic with expectations and start small.

1. Your system is fine, no need to overclock.
2. You can allocate folders as desired for the most part.
3. Rather than rack up a massive bill at the outset, it would be more prudent to test the waters, learn the program, and get your workflow solidified (you can always upgrade both programs and hardware at a later date).
4. System optimization is often a case-by-case basis depending on drivers and software installed on a machine. As things come online and you learn more, this forum is about the best resource to tweaking it.
5. As you mentioned Photoshop/Lightroom, I am not sure if this is as part of Adobe's Creative Suite or not (and which version)? If you also have access to Audition, the noise reduction tools there will alleviate most issues with "noise." If you are on CC, I would not recommend this specifically, as you can buy CS5.5/6.0 Audition outright and get the same tools if desired (with the CC version, you will pay for life).
6. The biggest "need" is an audio interface, possibly MIDI controller, and a DAW application. Again, all of these can be upgraded in the future, so a realistic approach would be advised.

Jim Roseberry
What you don't want is your audio interface sharing a Root Hub with another higher bandwidth peripheral (HD or SSD).  As long as this isn't happening, your USB audio interface will be fine.

+1 
 
That's it in a nutshell.

You should call Jim Roseberry before you commit to any PC. He's got the experience and answers to really help you.
http://www.studiocat.com/

I would recommend spending some time getting hands-on experience before pursuing major purchases of serious gear. Otherwise you run the risk of ending up with an expensive setup that doesn't properly suit your way of working. I agree with Mettelus. Take a piecemeal approach, one step at a time.