Is Snow Leopard Server a good candidate for everyday use as a main OS?
To answer your question, you can work perfectly under Server (given the above machine) in fact, if you disable some of the services, the OS X will be very similar to the regular version. On the other hand, you can always rely on Google docs and calendars, Remote Desktop and even OpenVPN if you really need an internal network. 

I mean, configuring the above (even on OS X Server) carries a lot of overhead, backup planning and maintenance. 

Focus on your "startup" and leave the unrelated tasks to others. Will having a server at your place (with all the electricity costs associated) make your start up better? earn money faster? 

Anyway, that's a topic for "startups". The answer is yes, that computer is more than capable to serve as a server for all those tasks and much more.