If an application is developed on VTScadaLIGHT and we need to develop more I/O than 50 could we run it on the paid version directly and add more I/O?

Yes and/or you can also request (via www site link) a 90-Day trial version with 5000 tags that runs for 4hrs at a time (meaning you can restart every 4hrs) . It includes all features with one thin-client. Applications created with this version can later be run on paid license versions without modification (though you cannot do the reverse).