Whoa, start by reading the Lean book again; you're questions suggest you are making a classical mistake made by too many entrepreneurs who live and breath Lean Startup. An MVP is not the least you can show someone to evaluate whether or not building it is a good idea; an MVP is, by it's very definition, the Minimum Viable Product - not less than that.
What is the minimum viable version of a professional collaboration network in which users create a professional profile visible to others? A website on which users can register, have a profile, and in some way collaborate with others: via QA, chat, content, etc. No?
A minimum viable product is used not to validate if something is a good idea but that you can make it work; that you can acquire users through the means you think viable, you can monetize the business, and that you can learn from the users' experience and optimize that experience by improving the MVP.
Now, that doesn't mean you just go build your MVP. I get the point of your question, but we should distinguish where you're at in the business and if you're ready for an MVP or you need to have more conversations with potential users.
Worth noting, MOST entrepreneurs are ready to go right to an MVP. It's a bit of a misleading convention to think that entrepreneurs don't have a clue about the industry in which they work and what customers want; that is to say, you shouldn't be an entrepreneur trying to create this professional collaboration network if you don't know the market, have done some homework, talked to peers and friends, have some experience, etc. and already know that people DO want such a thing. Presuming you've done that, what would you present to potential users BEFORE actually building the MVP? For what do you need nothing more than some slides?
It's not a trick question, you should show potential users slides and validate that what you intend to build is the best it can be. I call it "coffee shop testing" - build a slide of the homepage and the main screen used by registered users; sit in a coffee shop, and buy coffee for anyone who will give you 15 minutes. Show them the two slides and listen; don't explain, ONLY ask....
- For what is this a website?
- Would you sign up for it? Why?
- Would you tell your friends? Why?
- What would you pay for it?
Don't explain ANYTHING. If you have to explain something, verbally, you aren't ready to build your MVP - potential customers don't get it.
Keep working with that slide alone until you get enough people who say they will sign up and know, roughly, what people will pay. THEN build your MVP and introduce it first to friends, family, peers, etc. to get your earliest adopters.
At some point you're going to explore investors. There is no "ready" as the reaction from investors will entirely depend on who you're talking to, why, how much you need, etc.
If you want to talk to investors with only the slides as you need capital to build the MVP, your investors are going to be banks, grants, crowdfunding, incubators, and MAYBE angels (banks are investors?! of course they are, don't think that startups only get money from people with cash to give you for equity). Know that it's VERY hard to raise money at this stage; why would I invest in your idea when all you've done is validate that people probably want it - you haven't built anything. A bank will give you a loan to do that, not many investors will take the risk. Still, know not that your MVP is "ready" but that at THAT stage, you have certain sources of capital with which you could have a conversation.
When you build the MVP, those choices change. Now that you have something, don't talk to a bank, but a grant might still be viable. Certainly: angels, crowdfunding, accelerators, and maybe even VCs become interested. The extent to which they are depends on the traction you have relative to THEIR expectations - VCs are likely to want some significant adoption or revenue whereas Angels should be excited for your early adoption and validation and interested in helping you scale.