For the RAM you would really want to get 4gb which would put you towards the E520. The i5 M540 certainly shouldn't be slow for general use. Adding an SSD later on could also be a decent idea since I doubt your father needs lots of storage, this would make the machine a whole lot snappier.
I'd also be inclined to recommend looking at the ThinkPad T series such as the T510 and T520 (equivalent spec of the E520 and E430 respectively). The E series are good but aren't as well made as the T series. I wouldn't pay a fortune more but if you can get one around the same price I'd go for that.