For that sort of money you should be able to get a nice spec gti with decent mileage and all the minor common faults sorted. There's not much to worry about, there pretty bomb proof.
The engines can sound "tappy" but it's normal
Have a good look over the service history make sure it's been maintained and had the cambelt & waterpump replaced
If it's dsg then make sure that's been serviced when it should be
Check the front arches, rear arches and boot lid for the usual rust
Check the air con as it can be common to break
Check the rear high level brake light works
And all the usual checks you'd do when buying a car, tyres, previous accident damage etc etc
The mk5 gti ticks all your box's and more, In my opinion there's no other sporty hot hatch around for similar money that is better than a gti. It's a "Do it all" car. The build quality is far better than mk4 golf/mk1 Leon platform.
I've owned all sorts and have always been happy to go back to a Mk5. All colours are nice and it's personal preference really. You'll be fine going from the fiesta to a gti, it's a capable car in standard form but even a novice driver wouldn't have any problems in it. it would feel like a real upgrade from the fiesta (quality and power).
Get to somewhere local to you that has one in and get a test drive.