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.

Thanks!

Best,
Lukas