How to determine necessary storage space for packages + UM ?

I want to use a RB411AR for a hotspot incl. User Manager. On my x86-based hotspot, used for testing, I see, that actually about 200MB are used on the hard drive. But the RB411AR only has 64MB NAND storage.
How can I determine, how much storage space will be necessary for installation of all the packages, I want, and UM incl. its data base on the RB ?
How can I see, how much storage is really used on my x86-based hotspot for the packages and UM database ?

Download the packages you’ll install from the download page. Tally their size. It’s impossible to say how large the data store for the User Manager will be as that depends on how much data you put into it.