Student tablet for work

Hi all,

I'm a univ student looking into buying a convertible tablet for use in lectures, library etc. I would be grateful if you could offer me some advice.

My budget is 500€ max (surprise: preferably lower :D)
As indicated I am looking for a convertible such as the Asus transformer series because a necessary component is a keyboard as I will type a lot.
In terms of size, I am thinking of 10 to 13-inches

My primary usage of the tablet will be word processing (where the navigation with titles is important; I read that with some apps that doesn't work), but I certainly would also use
it for emailing, web surfing and reading (pdf's of articles, e-reading online) as well as sometimes a video. Basically, so far I have taken reading notes, written essays etc on a
rather heavy and big laptop which is quite inconvient, esp. when carrying it to lectures etc. I am now looking for an alternative. Following from that I would like to have software
with which I can process word docs (docx), powerpoint, excel and so on.
The issue is that I will also continue to use my laptop for the same purposes which runs Windows 7. It is very important to me that I can seemlessly switch between both devices (using dropbox...).
Apart from that I also own a Galaxy S3, ie an android device, but that shouldn't be an issue - I use it for different purposes (and don't use Google services frequently).
In terms of battery life I'm not sure what the norm is but >4h would be desirable. In addition, expendable memory would be useful (32gb seems too little). Similar holds for USB and micro SD slots.

My key concerns are the following: First, I need a keyboard. Second, my laptop runs Windows 7 and Office 2010. Given that I want to use both devices it seems sensible to choose a tablet with Windows OS.
But I am not sure whether Windows 7 and Windows 8(.1) will work together well, nor do I know about Office 2013 and 2010. At the same time, I wouldn't mind having an Android tablet in principle (I very much like the Galaxy Smartphone I have), but I'm not sure about the compatibility. So far the Asus Transformer Book (Windows 8.1 and Office 2013) or Pad (Android) seem interesting, but I'm completely open to other suggestions.