If this was 5 years ago I would have been hard pressed to not tell you to either go full out laptop or just get the apple device. Tablets running windows and android are now much, much further along. Honestly, there's not a single thing my ipad mini 4 does that I can't get my samsung tab 4 or my Samsung galaxy s 6 to do. If I'm being completely honest, I prefer my s 6 phone to my ipad.
I did some quick searches on both the apple store and the playstore for movie and music editing software. It was a shock because some of the same software is on both operating systems. Then, for kicks, I did the same searches for windows. In some ways the windows was better for that search, in other ways it wasn't so good.
So, really, the days of one being better then another, in my opinion, are over. It really only depends on what you like and prefer. All three operating systems link with bluetooth keyboards, if you don't want a laptop. All three do perfectly fine with accessability, though android and ios streamline it so that it requires less resources and doesn't read out file directories unnecessarily.
Here's another way to look at it. Does everyone you know use apple products? Are they facetiming all the time, or are they just using regular skype?
Not to be cold water on a cold shoulder, but picking based on accessability of the operating system shouldn't really be your deciding factors. Not any longer. We've come much further then that in the world of technology.

I use iOS and OS X with voiceover (and other accessibility features).
iPad is amazing once you learn how VO works with it.
A tactile keyboard would be nice, but an external one will do, or Speeddots, or braille screen input, or an external braille display/keyboard. Try and see what works is howit goes... With ipad mini vs regular sized ipad or ipad air - try and see what feels comfortable. Since screen doesn't matter, i like the mini.
I only use my mac for longer works or longer typing. I've got braille key stickers on the keys (around $20 from maxiaids) and those are really nice. My mac is from early 2013; i'm in no hurry to upgrade it. All macs come with voiceover, and also if you switch to macs, they also keep the value well so it's not a bad idea to get a se ond hand one, or keep yours for a few years and sell it to get something newer.
So that can help with the budget. With voiceover, scrensize is less relevant so if keyboard feels fine for typing size, 11" will be more affordable.
The only reason i need to get windows somewhere is to learn to use nvda (for work markets); i really don't want to learn again about the windows world security problems.

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I just upgraded to Windows 10 on my desktop, no touch screen though. Things are running well with my normal suite of accessibility tools (Zoomtext and NVDA). I heard negative reviews about the first iteration of Surface devices but it sounds like they have been greatly improved. A quick google search shows that it has the specs to run JAWS and that it can run full Windows 10 which is nice.

 

For $1000 though I think I would personally just buy a fully fledged laptop, but I'm not really a tablet guy. If you like the iPad and it does what you need it to then I'm pretty sure the accessibility will be better integrated on that device. I guess it comes down to what you need it for.

I'm using Windows 10 on an HP laptop that has a touch-screen, with NVDA. Personally, I use the touchscreen for almost nothing, because my laptop also has a keyboard, and I find that much nicer. However, it does work. Narrator isn't quite complete enough to be a screen-reader yet, but NVDA is fine. Remember, though, that you can get a keyboard case for the Surface. So if you go that way you get the best of both worlds.