Considering you're looking at potentially big, and have systems development experience, I'd suggest taking a look at Catalyst (it's perl, http://www.catalystfra

Considering you're looking at potentially big, and have systems development experience, I'd suggest taking a look at Catalyst (it's perl, http://www.catalystframework.org/ http://www.catalystframework.org/). The way it's designed, you can use any templating system you want (template toolkit, mason, etc.) and any DB backend you want. I've used it for some small projects and for some large projects, all with moderate success. Probably the best fit about it is that it doesn't force your app into being written a specific way. Once you have your foundation down, it's lightning quick for prototyping as well (and turning those prototypes into the fully functional, scalable system).