What features do you want to build into your Web App?

If you just want to display data, use read-only ODBC as the easiest way to access the data.

For any kind of data entry, the options depend on what you want to do.

Thank Kevin!

So if I just want to display data, I assume it's just a matter of establishing the correct connection right?

All data entry will be done through Sage, so no need to edit Sage database through web app. 

And what about setting up a notification function? For example, the web pops up a notification when a new SO record added in Sage, or after an order has been invoiced.

Appreciate your answer as always.

ODBC works from any machine on the same network as the Sage 100 server, with Sage 100 workstation software installed (and a valid login).  (Or if the version is Premium the data is in MS-SQL...).

Your path of least resistance is probably handling the "new" stuff yourself (build a mirror table, then merge in from the ODBC source...), and get to know what the different transaction data patterns look like in your query return results, then handle them however you wish. 

There are notification programs out there (Sage Alerts...) but they cost extra, add extra complexity to your solution and another potential point of failure.

You are competing with existing full featured functionality though, so you might want to look at what already is out there before investing in development time.  Sage is building an Office 365 connector (which has amazing potential but I've only seen demonstrations), XKZero has something for mobile too... and I expect there are others.

Thank you Kevin.