How does Cloud-Storage work?

HI there,

so i just had a discussion with my roomate about Google Fiber, the TB of G-Drive they offer to it and how we could extend our SkyDrive to switch with all of our data to the cloud, so we can use tablets next year which offer only limited storage to 128GB.

So we were wondering... lets say i upload 100GB to SkyDrive, Music, Images, Documents, Files - the whole stuff from my PC, and SkyDrive is integrated in Windows 8/RT/P8 how do the different devices handle the files?

I always had the feeling, my laptop and desktop will actually DOWNLOAD the content from SkyDrive whenever possible to have it instantly available on the local machines if needed. But what if the SkyDrive Storage exceeds the local storage?

Let's assume i have a 64GB Surface, and a 125GB SkyDrive. I have EVERYTHING i need on SkyDrive - so basically no local data on the Surface. Am i able to access everything on SkyDrive? Will it be downloaded to the device (which is not possible for everything) or will it be downloaded at the time when i want to access it? Same question for my phone and my laptop/desktop. Currently, my Lumia 900 downloads only when i want to open a file.

This is something critical for me as i want to replace my laptop with the surface pro and i want all files to be stored in the cloud to have them on my dektop as well. It would kinda suck if the tablets can't access all files and it sucks too if it gets only downloaded when i open it (no offline support then).

Also, if the tablet with windows 8 (not RT) downloads everything in the machine like my desktop, how will it react when the local storage is full but SkyDrive wants to Sync more and more..? And how can i "make space on the tablet" to access other, newer files from SkyDrive without delete files from the Cloud/SkyDrive?

I hope my english isn't too bad. Let me know what you think.