The moderators will be along soon to tell you that hardware questions are not appropriate for this forum :D but maybe I can sneak in a quick answer.
SD cards need to be formatted FAT32 and 64 GB is not officially supported by Garmin. You might get it to work, but it would be better to get 32 GB or less. To free up some space on your Zumo memory, you could move certain files to the SD card (like the map and junction view files). There are some folder and naming conventions, so do a little research or ask for some help (in other forums where hardware discussions are allowed.)
