to follow up about the database issue in general ...
Postgres would be a good consideration .. as its GPL (just like Mysql community) but it does support Geo-functions
and is project based. (gpsgate would run with just 30% of the tables .. as you can make real relationships between dynamic datasets..
things like moving a user between applications (as example) would be done with one statement.
geofencing or other GIS Functions are alot more easy to handle and cause less load.
just like in Oracle .. (but guess oracle is out of question because of the licensing)
Microsoft SQL does not support GISFeatures .. but in matters of compatiblity and performance .. MSDE MSSQL may be the best choice as its free because of franson NMEA Services are a .net application.
Backups are for WIMPS!
(website position GpsGate Powered)