Welcome to TTF!
As soon as you receive the 740, make an Explorer, not Home, backup of the unit's contents. If not sure how, see here:
https://www.tomtomforums.com/genera...4-how-backup-contents-your-unit-computer.html
1. Yep, both maps will live happily on the same sdhc mini card. Use Explorer to move the USA_Canada map folder to the card. The Western_Europe map will be installed on the card (see point 4 below)
2. When both maps are on the card, on your unit, Preferences-->Manage Maps, switch maps and you should see both listed. Just select the Western_Europe map. Actually, a more transparent way for this to occur is when you turn on your unit in Europe, TT will essentially tell you that, based upon your (then) lat/long [when it picks up your gps signal], the USA_Canada map isn't appropriate and offer to switch over to the other map itself.
3. When the European map is installed on your card (again, see point 4), the map folder will get created on the card. Nothing for you to do.
4. With the card installed in your unit, when you connect to Home (the software), it'll detect the card's existence and initially ask if you want internal or external selected, you pick external. Then go to Add maps, select the European map, purchase it and Home will initially dl it to the computer (all dl's from TT initially go on the computer) and install on the card. At least, it should. There is a bug in home such that despite the user selecting one location, Home tries to install on both or the other. Happens sometimes.
If indeed the unit comes when you expect, make sure you've checked here to see if map 850 has been released. It is due in a couple of weeks, so you don't want to blow your Latest Map Guarantee on updating to the current 845 just to find that 850 is released within a couple of days.
And always make another Explorer backup (different folder) whenenver a new map is installed.