Why?
It'd be far more helpful if you'd explain the specific quantifiable benefits to the OP of spending the extra money. Otherwise your post is kind of useless. From the OP's perspective we're all just random Internet strangers. We might actually know what we're talking about -- or we might just be blindly parroting something someone else once suggested for a completely different usage scenario.
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Yes, true, any price drops are minor and tend not to occur until the new models start to show up as refurbs themselves.
However, what does sometimes happen is the availability of older refurbs can go away. Consider the 2012 quad core Mac Mini.
Of these four, given what you've said, go with the 13" Macbook Air with 256GB.
Saving stuff in the cloud (whether iCloud or Dropbox or Google Drive or OneDrive) doesn't necessarily reduce your local storage requirements since all those tend to keep local copies of your files. They're better thought of as ways to easily share stuff between computers / locations as well as guarding (to a degree) against data loss through device theft or drive failure.
If you're handy, consider the possibility of an aftermarket drive replacement.
Otherwise buy as much storage as you can afford. What is your current usage? Between 128GB and 256GB I'd definitely go for the latter unless you only have 20-30 GB of stuff. With video it'll likely be higher of course. Still, your storage needs aren't going to go DOWN over time, are they?
Can't really help with specifics on #2 other than to say that my 2011 MBA 13" still is perfectly fine for web surfing, document editting, a little bit of Lightroom, email, etc. The CPU differences aren't likely to be visible to you unless you're doing heavy CPU load stuff. I don't do any video so I don't know how much load that'll create.
The 11" MBA screen is kinda small IMHO. It's a great compromise for a highly portable device, but you'll likely want a 13" display if this is your primary computer. Will you use an external monitor?
The MBP you mention probably has a spindle drive. The others have SSDs. MAJOR difference in user experience. Stick with SSD or plan to replace the spindle drive with an SSD if you buy the MBP.
Now with all this said, while 4GB is pretty usable on a MBA for the stuff you describe, the video editting might be too much for it.
I'd really recomment seeing if you can try it out before buying, or ensure you have the ability to return the computer if it isn't usable.
See
https://forums.macrumors.com/threads/how-much-ram-do-i-need-in-my-macbook.1756865/
