How can I get feedback from potential customers for an inclusive Christmas vacation concept as part of the customer development stage of my startup?

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.

Hmmm? This is a tough one because your product is so wonderfully horizontal, meaning it applies to a very broad set of cases. I'd slice and dice in two directions. First, I'd think about the general process of collaboration on a document, for example: a) drafting - are two people actually writing the words together? I personally don't like this. b) first read through together staying on the same sentence or page, c) editing together, etc. Second, I'd think about industries or verticals or contexts, such as in a Legal setting, in a Tech Documentation setting, in a coding or XP dual programming setting, in a social media post drafting setting, and so forth. Check out: https://medium.com/look-what-i-made/fd48c3b412bc Seems to be evocative of what you're doing, but targeted to one specific use case of "pair programming".

Find apps that are B2B and go to the review sections. Specifically going to Google's play or Chrome store and look at reviews and follow them to Google+ to engage. I took that same angle for B2C app I was building last year. Check it out. http://blendah.com/post/37331434653/lean-startup-hack

You should be so lucky that someone will steal your idea. The truth is that its all about execution and not ideas. Facebook wasn't the first social network, they just executed better. Same for Instagram, Yammer and Airbnb - all Billion dollar companies built in public.

It really depends on whether this is ultimately a top-down or bottom-up approach and to what extent the end-user experience is compelling enough to act as a forcing function to enterprise adoption. A bottom-up distributed mobile app must be both viral and incredible engaging. Without proof that you have that (or absent proof, strong conviction) most are better off attempting to sell top-down. Happy to talk this through in a call