At this point I'd seriously consider 64GB. You should be able to get at least two solid years of compatible iOS updates out of a Mini 2 at this point, and you'll likely be missing that extra space before it's over. There should be enough Apple refurbish units for sale by now that you save at least half that extra $100 back. Refurbished iPads sold directly by Apple are 'like new" and come with full warranties, btw.
To speak to your other concerns. Expect it to be different. Especially the way files are handled. While the addition of iCloud Drive has made things a bit more like a computer file system, it's still not the same. Apps own the files they create and use, and you have to go through an app to add/change/delete them.
In general, almost everything you are used to doing on Android is still doable, but you may have to get used to another way of doing it.
The main advantages of iOS over Android (in my opinion) are these:
(1) A simpler and more standard UI. Android has made great strides in the last couple of years, standardizing the UI experience. It's a lot closer to iOS quality than it used to be. Unfortunately you need a fairly new Android device, and a vanilla Google install to get the full benefit. Not an option for a lot of older Android devices. iOS on the other hand has gotten more complicated. It's still about the same on the surface, but a lot of complicated features now hide just below the surface.
(2) Updates. You may not always want them, but unlike Android the come out for pretty much every device they can run on, and will support as many new features as the device can handle. Because of this there is wide adoption, and you can expect your device to run almost all the newest apps; if not perfectly, the usably. The draw back is that the pressure to update is much higher. Something that tends to be a problem when you've got an older device and don't want to sacrifice performance for more features.
(3) The App Store is still the best source of apps both in quality and quantity. Google's made a lot of strides, and some of the features of the stores themselves leave Apple's store looking a bit dated; but apps still tend to come first for iOS and (in my opinion) iOS apps still tend to be more polished and feature rich. There are exceptions, of course. Because of Apple's more restrictive policies and developer rules there are some apps you simply wont' find in the App Store. Interestingly Google's been getting a lot more restrictive lately, as they discover the downside of being too open and easy.
(4) Support. There are probably a few Android vendors and merchants with comparable support and customer satisfaction scores, but none of them are better than Apple. Is it a perfect world and everyone goes away happy? No. Customer utopia is still a fantasy.
(5) Personal preference: I just like iOS better than Android. I have a first generation Nexus 7 running whatever version of Android it can (I'd have to check to be certain what that is). It's usable, even good, but I like my iPad better. The Nexus sits by the bed in the off chance that I might want to read a Kindle purchased book. I almost never use it, even when reading in bed. Newer hardware with a better screen and the latest Android version might change that, but probably not by much.
Final Note: Every one of these points has an up side and a downside. All tablets and operating systems are a series of compromises, and to be excellent at one thing they generally sacrifice some other desirable trait. It's all about finding the device and OS that compromises in the way that fits you best.
All I suggest is that you give the iPad a run. Don't 'expect' it to work the way you are used to, or allow yourself to get frustrated trying to beat it into doing things your way. Play and explore for a week or two, learn how things work in iOS, then decide whether the change fits you better.
. . .Bla bla, bla {more pedantic bull} etc. . .
Ok, done.
how do you deal with so little memory?
