> Even without promotion, I get more requests for work than one person can commit to while offering dev services at market rate.

That's wonderful situation to be in :)

> The challenges I've experienced relate more to the business and administrative functions and in general optimizing the amount of time spent on non-billable things.

This is a tough one and it's something i struggle with too. I take it you already have the usual suite of apps to help (xero/freshbooks, timely/toggl, hellosign etc).

> One analogous challenge a contractor faces is figuring out how to make the jump from software contracting into technical consulting.

Also tough, but more familiar. This jump always feels like a matter of specialization to me. It usually means leaving the variety of being a generalist behind. Luckily there are many ways to specialize: Functional. Technical. Process Engineering. You can even combine these specialties.

The less technical specialties require more nuanced proof of your abilities. It's definitely a good idea to keep notes of applicable project, moments, achievements.

I was a consultant for 7+ years (taxes + tech), although not an independent one, and i'll say this: it takes even more non-billable time to do it right.

Do you have special skill set?