Many of the target groups you listed have their own proprietary contract processes/apps in place.

Low hanging fruit may be independent consultants, freelancers, and small business owners. They deal with contracts all the time.

If you are going to continue targetting real estate, financial, and legal firms; take a few hours and interview those you have contact within those fields. I guarantee they have frustrations with their existing program and would give you an ear-full to position your product correctly.

I'd love to help more, if you have another question, or want more specifics, feel free to book a call with some times you are available to connect.

To your success,
-Shaun

Add service agencies (Marketing, Creative/Branding, etc) and B2B sales teams across the board. Starting list looks good. I would suggest the highest value (and level of competition) would be in legal, finance, and general B2B sales.

I think you already answered your own question. Start with the market you know - investment banking.

This is clearly an extension of virtual document rooms. Start there. Who buys VDRs? Target them. Figure out which conferences Merrill and Intralinks attend. Go there as an attendee, corner a few people, and figure out who else has the same problem. Sell a few of them. Then buy a booth at the next one and set up some real meetings.

One huge trick to SaaS is to stay very focused on an achievable, small market first. Then, as you get traction, start expanding you markets and capabilities. The biggest problem in SaaS is that either your development team or your sales team is always going to be behind. It's much more likely it'll be your development team. The more markets you add just creates more initial complexity and slows down your developers.

Build a tightly defined product and market it to one market. Then create derivative products and expand your brand.

I'm happy to chat through more strategy with you if you'd like to go deeper, but I think you already have the first market figured out.