I can't speak on chromebooks, since I wouldn't go that route. It seems a rather useless device without an internet connection.
If you're interested in a tablet, you have three choices. Windows 8, an iPad, or some flavor of Android. I'd stay far away from Windows for this, and I say this as a Windows fan, but that's in the context of a real computer. This leaves you with Android, which is owned by Google, and iPad, which is an Apple product. Apple makes both the software and hardware for its products (generalizing here, for you purists), whereas Google makes the software (Android), but has very limited hardware exposure, the Nexus being about the only one. A ton of companies make tablets (and phones) that run off googles Android software, and a tablet is really not much more than a bigscreen phone. Many tablets and iPads have the option to come with cellular service as well as WiFi. Much of this you might already know, I'm just trying to be somewhat thorough.
No matter what brand of tablet you would get, they should all have bluetooth (check before buying of course), and there are many bluetooth keyboard options available. Not many people use them, and 90% of all I write on these forums, including this post, is done by speed-pecking on a glass screen. Once you do it for awhile, it's actually fairly efficient compared to a tiny phone screen IMO.
Android will have more of a file directory, if you're used to sifting through folders and moving documents and pictures around by actually moving the files themselves. Apple does not give you this option. You will not have any direct access to your files what so ever, unless you start jailbreaking your system and getting crazy-nerd all over it. But then you wouldn't be asking this question, so skip ever seeing your files with apple. (Again, generalizing. Purists will ante up work-arounds, special apps, tricks, etc.) Apple has very proprietary software and they don't want anyone to see it, touch it, deviate from it... Nothing. You do what they say. If you buy an app, and they later deem it innapropriate, they can wipe it off your device. They are very control hungry. That being said, the iPad is built like a brick house and the software runs smoother than most anything else you'll find.
With no real user level file directory, there's no effective way to manage external storage, which is why you won't find expandable SD card ports on apple products. Once again, there are tricks to renaming images so an SD card can use an adapter in the charge slot, but it's very unwieldy. You certainly won't be filling SD cards up with movies, music, pictures, pdf manuals, oddball backup files, or any of the other storage solutions you may be accustomed to, and swapping it around in different devices. Although with android, the file system is essentially just like what you're used to with windowa xp. I can pop an SD card in my XP Netbook, drag files or folders of any kind onto it, even backing up my Windows programs, then remove the card and put it in my android device and it's all right there in the file directory, just like windows, albeit a bit adapted for the smaller screen. Tablets don't run multiple "windows" after all, it was just one window at a time only until recently. Even if a file type is unknown to android and it can't run it, it will still be viewable, moveable, deletable, renameable, etc.
There is apple, and then there's everything else. This can be good, or bad, depending on your point of view. Apple is just a very controlled and closed environment compared to the open source nature of android. A big bonus to this lockdown mentality apple has, is it's also very safe and fairly virus free compared to the android environment. If security is a major concern, and file management is low priority, then apple would be a good move IMO.
As far as downloading programs, you don't. It's just like a phone. You download and run "apps". Yes, they are "programs", but tablets are different animals. So what I would suggest, is take a trip to both the "apple app store", and "Google play", and look through a variety of apps they offer. Most developers make apps for both platforms, but you might start getting a better feel of what the different environments are like by looking at some screenshots, etc.
That's about all I have on tabs, I use my XP netbook for more detailed spreadsheet work, and I might boot up my quad core, dual vidcard/monitor desktop if I need to run my antiquated printer (since I don't game much with it anymore, which is what I built it for), but for web, shopping, email, banking, bills, social, minor spreadsheet work... It's all tablet anymore.