Honestly, I think that is the best approach. Because the market is so broad, it will be hard to reach out to everyone based on company size. I am currently focusing on 2 segments incidentally one of them is dentists the other is accountants.
Thank you for the links.
Have you thought about targeting a sub-niche, to try to get some traction, before going broad?
For example, Dentist's offices: if you were to call and visit a few local dentists, see if there are any customizations that would help them specifically (like recurring appointments a year in advance, etc.) and then brainstorm with them to see how they would recommend you advertising to their colleagues.
Once you get some traction in one vertical, you can leverage it to the next one.