Your laptop may well be able to take up to 4g Ram. 160g h/d is well sufficient for wins7. I would suggest, if your laptop can take it, to buy 2x2g ram making 4g memory then install wins 7 64bit OS. As you are a light user 160 is more than enough.
Sony Xperia Z5 review: Hands-on with the phone which the Z3+ should have been