My personal opinion...
I've had different size laptops and tablets. Yes, it really depends what you will be using it for... And in Android and Windows land, brands and models all have different pros and cons.
For mostly info consumption, my 8" Samsung has the right mix of screen size, weight, sound, etc. for me. However, using the on-screen keyboard on anything between 6" (Swype style) and 10" (normal typing) is slow, and even the 10-12" tablets on screen keyboard is much slower and full of mistakes compared to a regular keyboard. Also, taking along a separate keyboard bulks up the carry load that I hate bringing it along... Plus charger and or batteries.
I think most of the things you listed can be done fine with a tablet, and Apple's tablets are really nice... as long as you don't mind the price of accessories and external storage options. Also keep in mind that often tablet browsers are mobile browsers.
That being said, if you don't plan on inputting a lot of work, and info consumption is your primary use, a small tablet is much easier to lug around, hold one handed, etc.
Personally, (although I have a 3 monitor desktop setup for the home-office) I use the 8" tablet watching videos, reading the news, controlling the TV, Skype, and other info-tainment when lounging around the house. Then I have a large screen smart phone combined with a 11.6" Windows 2in1 for work and when traveling.