I'd be wary of Dell. Used to be when everything I got was Dell but in the last few years have had two laptops (for my daughters) and one notebook. The former both fell apart after a couple of years of light use and the batteries died after a year followed by both machines dying terminally with disk failures within a couple of months of each other just after two and a half years. The notebook the battery died after a year. We replaced them with Sonys bought from John Lewis and they have been soldiering on doing a sterling job now for four years. We have three other Sonys lying around dating back over 12 years now for the oldest. They are all still in good shape despite having a hard life being carried around every day in a Brompton bag, the batteries are still just fine and apart from being a bit slow now being old machines with old software and processors, are still perfectly usable laptops.
The Dells were actually using Sony batteries, and I assume Seagate disks. I had a similar generation of Dell and Apple and they did about the same.
Don't pay for the extra RAM, do get a good CPU. Extra RAM is cheap, do get 64bit Windows. RAM is cheap and easy to add later, it will give a much needed speed boost at the 18 month mark. Hard disk isn't much of an issue, an external drive is more useful.
I'd buy from John Lewis for the two year guarantee, most actual computing brands are pretty solid these days. Everyone has their horror stories too. We have HP, Samsung and Toshiba at work. The Toshiba are just exquisite, but bonkers expensive, the HPs are our portable dev environments (and for £450 came with Dre Beats), the Samsung is a demo machine for being £550 and coming with a NVidia chipset.
As the others have said, any mid-ranged laptop shall be suitable and the more RAM the better.
One thing that I do suggest, is if it is going to need to withstand a fair number of knocks or small drops then in past experience Fujitsu Siemens seems to survive the best... yes, I've dropped my fair share of laptops.
Extra RAM is a false economy as you tend to pay a premium for it, for 1GB difference you can often purchase 4+GB and install it yourself.