Doesn't matter if you're using Windows 7 or Windows 8.1 anymore, after the Windows 10 switch we'll all be using the same operating system, so you don't need to worry about buying 7. I wouldn't recommend spending money on Office either, you can get Open Office for free here: http://www.openoffice.org/
And as far as laptops go that would be dependent on factors like screen size, brands, estimated battery life, and so on and so forth.