Your Garmin help, please

^^ You can, but there's a limit on the free on-line map-generating tools, and none of them will produce an all-Europe map. I don't think there's a technical reason why you couldn't have an all-Europe OSM map - I just couldn't find anywhere to download one, or any way to create one. In the end, I decided that spending 66 quid was better than wasting any more time trying to avoid having to.

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?