I think you've got it down pretty well. I would use a built-in SD card reader unless your computer is really old with slow ports. In almost all cases, it will be faster and less prone to error if you create the card in the computer, then put it in the GPS.
I'd suggest installing these two free tools, they are really helpful for managing Garmin Devices. Unfortunately, the author had a serious health problem several years ago and is no longer updating these apps, so there could be compatibility issues with newer operating systems (especially on the Mac).
https://www.javawa.nl/gmtk_en.htmlhttps://www.javawa.nl/jdm_en.htmlThere's a less-obvious but important thing to check on your cards. Use the Device Manager program to check the total number of map segments on each card. See this info from Garmin's site, which says your GPS supports a total of 3000 segments.
https://support.garmin.com/en-US/?faq=rFMnK0E1GOAC7SG3rGhV0ADo not create a card with more than 3000 segments or it won't work properly. Some maps or parts of maps will be blank if you exceed the limit. Impossible to predict because it depends on the maps you are installing.
But the segment limit applies to ALL files on the GPS - the SD card PLUS internal memory. So you need to add those two numbers and make sure it is less than 3000. There's no standard size for a segment, it's up to the map maker.
Typically, you will hit this invisible segment limit long before you fill an 8gb SD card.