There's no reason that SQL Express will not work with the GRA software. You can do a search for something like
running sql express in production and you'll see the potential pitfalls of using Express in a production environment. I'm not sure any of them are that critical in a 1,500-participant program.
For an example of scale - our summer program last year:
- 77,000+ participants
- 43+ million points
- almost 116,000 completed challenges
- 890,000 badges awarded
- final database size: a bit over 1.3 GB