I do similar work. I don't always find that inbound startups and founders know as much about how to really do an "MVP" as their using the language of Lean Startup would suggest. There are certain pockets in major startup markets that do understand the language, but in those cases you're more likely to find a technical co-founder who does this work.

The biggest challenge in a business like this is going to be your business development and deal flow (i.e. "gig flow"). Yes, it's a compelling concept, but it's going to be all about keeping the gigs flowing and as a small shop the biggest challenge is going to be doing enough business development work while also doing the production work yourselves. I have done a lot of thinking and work about this for freelancers, myself included. I have some good solutions if you'd like to chat about it.