Automatic ebook download ?

Hi all,

I am using a Microsoft Surface Pro 4 as a reader, mainly for comics and magazines.
My library is huge (600 GB+) and I can't (and don't need/want to) copy it entirely on my Surface.
The library currently resides on a shared drive and I access it from my Surface and Calibre which opens it directly through a network (unc) path.

What I would like to find is an easy way to download (copy) locally the books I want to read when I am not connected to the network drive.

Ideally, I would like to be able to add a "to download" or "to read" tag to the selected books and get them easily (if not automatically) downloaded to a local Calibre library on my Surface Pro.
All I would have to do then is to switch to the local library when I'm offline.

How can I get Calibre to work this way (or something approaching)?

Thanks for your help,
Patrick