I visited your site. It is simple and straightforward. But something surprised me: I was expecting the likes of Accenture, E&Y, Genpact, someone like that, as a target market (internal solutions may exist in these companies, but I have never encountered them, always a cropped screenshot then copy-pasted document, and this has been thousands of times).
Smaller clients does make sense: your target market as smaller clients could knock the pants off larger clients (in a small, accounts payable way) in terms of style an appearance. Can you get your clients to integrate to SAP or other accounting systems?
In direct answer to your questions (Firefox on Mint Ubuntu/Linux/GNU):
I am not a fan of the typography. For polish, add a bit of line-spacing, in the bullets in particular.
Perhaps separate each section (topic area) of the front page with a different background (I know this is terribly Bootstrap, but hey).
Registration: Do not advertise a lack of credibility / assuredness. But do not demand intrusive personal information (turns off both corporate types trying something out and technologists for a myriad of reasons).
I did not detect an option for HTTPS. This is a must for any site proposing dealing or storing financial or client information.
Try a start up form on the front page, or a direct shot of a demo. Include use cases and customer comments (do not fake these, make them checkable - check with your commenters this is OK beforehand).
Word of mouth counts for a lot, especially in professional circles that do not use social media (other than perhaps talk to one's family and old friends). Get a foothold with some oldskool businesses, then when you have a little coming in as revenue seek ways to pump it up (when you've shown it is a credible service this is orders of magnitude easier, in the most unexpected ways).