Hi WicklowMan2013,
So iCloud is a synching service across devices, so you must have enough storage on each device to hold all the desired synched "items" between devices. What I would suggest you do though is this:
- Look at how much of your Photos, Music, Movies, documents (all), etc., that you have synchronizing between your iMac, MacBook Air, and iPhone through iCloud.
- How much of them do you really need doing that?
- You say you only have 11GB of space on your MacBook Air and yet, 360GB available on your iMac; what is the full disk capacity and how much can you safely offload to an external drive? This may be a case of you having to juggle around files for a bit.
- Do you have an external drive you can move less frequently used stuff to? You can move large things like your possible Photos Library, Music Library and Movies Library off your MacBook Air's internal drive to the external drive.
- Are you comfortable going into your iMac, MacBook Air, and iPhone iCloud settings and turning off synching of the biggest culprits?
On your Macs, go to Apple menu > System Preferences > Apple ID > iCloud and look over both Photos and the iCloud Drive Options, can you turn off them? You can (for Photos) turn off the sync and have 30 days to download any photos and videos therein (or a faster solution might be to connect your iPhone and iPad by cable to your Mac and have them synch their Photos to your Mac's Photos and then delete the iPhone and iPad versions.
On your iPhone, go to Settings > your Name at the top > iCloud > check then what you have enabled and synchronizing to iCloud. Also go into Manage Storage and review what you have using up space therein.
I know this is a lot to take in. What I can suggest is, take a hard look at your reasons for using iCloud and what you really need to have synched across devices. I say this as, once you know what you really need and know how much space that takes up, you can start to formulate a plan (we are happy to offer advice here on the forums) of how to get there and save you time, money and frustration.
So, what I suggest you do is:
- Take a screenshot of your current MacBook Air's storage setup (Apple Menu > About this Mac > Storage) and post it back here. Do the same with your iMac
- Do the same with your iCloud Storage (Apple Menu > System Preferences > Apple ID > iCloud Storage.
- Break down your reasons for using iCloud and also, what you use each device (iMac, MacBook Air and iPhone) for. Are you duplicating this across devices that may be (though nice to have) not the best use of either the device's space, capabilities and/or iCloud resources?
I know I have put a lot on your to digest. Take it with a grain of salt, breathe and when you're ready, write back. I am sure, we in the community, can offer advice to make you both love your Apple devices again, use them well and not drive you crazy.
Cheers,
Anthony