Usual advice, any current computer will effectively be overpowered, so if you want to pay more consider the screen and keyboard, form factor, battery life, those kinds of things.
People will, for some odd reason, fight to the death over Win vs. MacOS. I like Macs, obvs, and I find they do just work. Someone will be along in a few minutes to say the same about Windows. Linux is perfectly functional, but you're still sailing close to the command line at times.
There are various free office suites like LibreOffice. They work fine unless you need the full features or you are collaborating with other Office users. I find subscription products a con – there are standalone versions of Office available, but they're not cheap and the licences are for one machine.
Sale of goods act covers computers, so you should expect problems to be reasonably put right even outside of the warranty period. That said, there's some comfort in actual customer service and quibble-free fixes, and it might be nice for there be a couple of bricks and mortar stores left on the high street.