As I understand, advice on specific equipment is outside the scope of this forum. However I can perhaps give some general advice on the concerns you may need to have when making your choice, assuming your main purpose is to use the instrument to practice piano technique.
First of all, DON'T make your decision without trying the actual instrument you may be buying. Much like an acoustic piano (or perhaps more), the feel of the keyboard varies considerably by manufacturer and model.
The sound also varies a lot, but it's perhaps less important for practice. It will be extremely difficult, not to say impossible, to further your studies beyond a certain point with a digital piano only anyway. So if the keyboard is suitably responsive, for general technical practising such as scales and drills, sound is not so important, as for subtle performance practice you will need an acoustic piano eventually at some point.
If you have been playing for five years, you have enough sensibility your self to try out several instruments and judge for yourself if the overal feeling and response is to your liking. Try to go to a shop and try different models to see if the price difference is worthy (for you).
Second hand digital pianos also suffer from heavy use, so always try it before commiting.
Regarding features, if your purpose is to study piano, put your money on the best responsive keyboard you can afford, forget about multiple sounds, effects, integrated sequencers and song recorders, etc.