Gosh, there is no one best answer. The answer depends on what you're building. That said, I'm a great believer in rapid development and getting a beta in front of customers fast so you can begin the learning curve journey validated by experience rather than one's projections or suppositions. The fastest prototyping I know of is a combination of Firebase.com for the backend and a more general approach on the front-end to cover more mobile platforms, so HTML5 in combo with Ruby on Rails. Again this is for rapid pilot to fully understand your needs. Once you're sure of platform, I'm still a bit more biased toward native mobile development focusing on delivering an awesome app on iPhone, then porting to Android and others.

After drafting the above answer, I was reading the latest Gartner trends report and found information relevant to the question:

Gartner Identifies the Top 10 Strategic Technology Trends for 2013
Analysts Examine Top Industry Trends at Gartner Symposium/ITxpo, October 21-25 in Orlando

Mobile Applications and HTML5
The market for tools to create consumer and enterprise facing apps is complex with well over 100 potential tools vendors. Currently, Gartner separates mobile development tools into several categories. For the next few years, no single tool will be optimal for all types of mobile application so expect to employ several. Six mobile architectures – native, special, hybrid, HTML 5, Message and No Client will remain popular. However, there will be a long term shift away from native apps to Web apps as HTML5 becomes more capable. Nevertheless, native apps won't disappear, and will always offer the best user experiences and most sophisticated features. Developers will also need to develop new design skills to deliver touch-optimized mobile applications that operate across a range of devices in a coordinated fashion.

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".

"What recent work activities have been most fulfilling for you, what has gotten you excited or "lit up"?

This question leads into the territory of Culture and Mission. It'll underpin the dialogue to evolve an explicit Mission from the bottom up, and will also serve as a filter for employees to notice whether what they are passionate about fits with the group mission or passion.

"What is the most positive action by a fellow employee that you noticed?"

There is a cultural bias in companies for employees to spend a lot of time complaining (or whinging as the Aussie's say) which focuses attention on negativities. There is a need to systematically counteract this bias, and asking for a focus on the positive or "bright spots" will do so.

There are several valuable, practical, and actionable viewpoints offered already. I'll bring a bit more of a long view to the broader question of team building, and suggest some references / best practices that have been incredibly helpful to me repeatedly over several decades.

Startups have a lot of unknowns and a lot of raw talent that is learning along the way. There is a predisposition toward trial and error, when often, in the end, it's easier and less risky to invest your time in understanding best practices and adopt what fits, leaving out what does not fit.

Culture
On this thread, Glenn Nishimura posted: "… it's imperative to be clear on your company's vision and values." Former IBM CEO Lou Gerstner said, "I came to see in my time at IBM that culture isn't just one aspect of the game – it is the game." Defining the Culture explicitly, which includes Vision and Values, is the next step after having a great idea. To learn enough about this to do it well, check out:

1. 15 minute TEDtalk by Simon Sinek essentially on Vision and Values - WHY, How, What.
http://www.ted.com/talks/simon_sinek_how_great_leaders_inspire_action.html
If this resonates with you, drill into his body of work, including his book "Start with Why" or his website http://www.startwithwhy.com

2. Book - Fifth Discipline by Peter Senge (1990 & revised 2006). I read it when it came out and have re-read it about 5 times. It's a great handbook for "programming" a culture that can learn and adapt well because it looks at the context, problems and challenges, from a system theory viewpoint, to invite reflection and response, rather than reaction.

Lifecycle
The people and talent you'll need will depend of course on your situation, but there are some guidelines or generalizations based on studies from the lifecycle of a business. The thought leader in this area is UCLA's Anderson School professor Ichak Adizes.
see http://www.adizes.com
I first read his book in the 1982 and have used it since to figure out what roles are needed and how they evolve at the various very early stages. The website is geared more toward large companies, but if you just study his introductory points, you'll see how applicable it is to startups. Indeed, Dan Martell's post suggesting a certain "great team" is supported by the Adizes' thinking.

To gain a preview of coming attractions of the startup journey and some great practices along the way, I recommend the story of 37Signals.com in the book "ReWork" by its founder, Seth Godin.

To get into the head of an entrepreneur and the emotions, vision, and delusions, as well as to see a great example of "prototyping" I suggest the enjoyable film "Tucker, the Man and His Dream".
See http://www.imdb.com/title/tt0096316/

I hope you find this helpful.