With a drive centre and faceplate you can do a fait bit, Spindle work certainly.
Not sure how long wood turning chucks have been commonplace, not forever so there are ways to make things without one. Google for turn a bowl without a chuck or turn a lidded box without a chuck.
Long term you will want one, but as Phil says 18mm is unusual. Meantime why not turn a few things before spending extra ££ then you get an idea of what you really need and get to appreciate your machine's characteristics. All machines have some limits, no point thinking about a big hefty chuck if the lathe bearings aren't up to it or big long bowl gouges if the motor doesn't have the power for fast cutting.
Not trying to put you off, maybe build up gradually so you don't spend on things you don't need straight away.