Hi Ellen,
With what you want to do, your setup can be achieved with the right type of configuration.
If you checkout the tutorials tabs, and search the questions tab, you will find many users who have requested similar types of setups that have been achieved.
For starters i would recommend checking
This should give you an idea on how to have a setup and have data centralized at one location.
As for keeping up with coffee card. this is doable, but in a slightly different variation to your system. I personally haven’t tested yet but I intend to test it for coffee shop clients I intend to attract in the near future. Just waiting for the release of V5 
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If you get stuck anywhere, samba forums have a very active forum with it’s developers responding and community users responding and helping all the time 