Your Garmin help, please

How much of Europe will you see in one go though? Why not just create the three smaller ones (if that's required) and keep them on your SD card?

Possible, but a right ballsache as you'd have to create each map separately and manually, while making sure that collectively they included everything. The trouble is that the map generating sites are set up to do country-by-country maps, whereas the continental rides I do have a distinct tendency to cross national boundaries because that's where the big interesting lumpy bits are. So for me faff>benefit given the relatively modest price of the Garmin mapset. But, as ever, YMMV.