Great to hear to have success, although somewhat limited. At least you will be able to do your trip with some guidance
When you have the time, give garmin a call. They should be able to help get all of Europe onto your unit. After all, you paid for it, you should be able to use it.....
I don't think you need a larger SD card. All of CN Europe should fit onto your gps.
Regarding Mapsource/BaseCamp... I guess I'm old school. I also use topo maps not created by garmin, and have had to use a modified version of Mapsource to get these to work. The modified version works well with the latest CN North America too. I don't know if BaseCamp would work with all the maps I have.