Are you at risk of your competitors copying your features by building MVPs?

It's really ill-advised to solicit your vision from anyone. In my 20 years of building, investing and supporting tech companies, I don't know of a single success story that has it's origins in someone with your approach. Running a tech startup is incredibly hard. It demands sacrifices few are truly able to make and come with it tremendous risks that most people are unwilling to take. It sounds to me as if you want the startup life because you have an impression of what it's about but haven't yet experienced it first-hand. I'd encourage you to first join an early-stage startup. Developers are incredibly in-demand. Find an entrepreneur who has some experience, funding and a compelling vision that you believe in and get to know what the journey is really like.

Check out https://www.balancedpayments.com/ They are made for marketplaces. Airbnb CEO among others invested in them and they have some of the best pricing/payout fees. Also some good info on http://www.collaborativeconsumption.com/2013/10/08/online-marketplaces-are-hard/ One of Balanced Payments co-founders is writing this blog series on marketplaces.

It's very important. (first, read this article by Josh Breinlinger - http://acrowdedspace.com/post/47647912203/a-critical-but-ignored-metric-for-marketplaces) The way you achieve success in a marketplace is by driving liquidity for both your supply & demand. Demand-side Liquidity = When users come to your marketplace, they can achieve their goals. Supply-side Liquidity = When supply comes to your marketplace they can achieve their goals... which are almost always to make money. If you're making a large amount of your supply-side users a full-time income, then you're helping them achieve liquidity. Now it's not so black and white and it doesn't always have to be a "full-time income." It depends what their goals are. E.g., 1) At Airbnb, renters aren't looking to quit their day jobs and become landlords full-time... they're just look to earn a substantial amount of income to offset their rent, mortgage, etc. So in this case, I would probably goal on # of renters that earn >$500 / month... and (in the first 1-5 years) try to grow this number by 10-20% MoM... and maybe by just 5% once you're in the mid-high tens of millions in yearly revenue. 2) At Kickstarter, the goal of the supply-side is to get their project successfully funded. They don't care if the project creator is "full-time"... they just want to make sure they meet their funding goal. This is why they talk about their 44% project success rate all the time - http://www.kickstarter.com/help/stats 3) At Udemy, our instructors want a substantial amount of their income to be driven from their Udemy course earnings... so we look at how many instructors are earning >$2k / month.

I have built several multi-million dollar businesses using (2) very simple questions: "What makes you say that...." and "Tell me more...." No matter what someone says to you, you just keep asking one (or both) of the questions. If you do it 4 or 5 times in a row you'll learn everything you ever wanted to know.

Focus on the more difficult side of the marketplace. For instance, if you think it'll be easier to get suppliers, then focus first on getting buyers - always be working on your toughest problem (aka your biggest risk). You'll find some great blogging on Marketplace and Platform topics here http://platformed.info (read the ebook too!)