I have a similar problem, bad eyesight, so that's why I went with the Note 2.
I can't get the text in the Facebook app to a comfortable size, so I just use the mobile web version. It's pretty much the same.
With Twitter I use Tweetcaster as it has a variable font size slider.
I've set Chrome as the default browser and in the settings you can set a custom text size, which works very well for me, and you can double tap the portion of the screen you want to zoom in on.
Good luck.