Not a fan of 3 door cars, the doors have to be longer to allow access to the back and they’re awkward to open in confined parking spaces. Getting in and out of the back is also a pain (literally) as you get older. Just got rid of wifey’s 3 door Fiesta for this very reason, it was getting on a bit but was still in great condition.
The current crop of small turbo engines seem to do the job very well. I’m sure the manufacturers have designed them to give decent longevity so I wouldn’t be worried on that score.
I wouldn’t worry about tax bands, when you calculate the total cost of running/owning the car it makes little difference.
I favour buying used cars from the main dealers thesedays, plenty of choice and the cars are usually very good. You might pay slightly more but as a private buyer you can haggle for stuff like free servicing, I’ve done that a couple of times.
Always choose a colour that’ll sell well in the future, avoid girly colours or fashion colours.
Paul