I love kettlebells – they’ve worked wonders for me, i’d recommend going to a class for a while to get your technique properly sorted and an idea of what weights you need before shelling out – as previously mentioned you might find that you progress quite quickly as your core strength builds.
To give you an idea, i’m not very big (5’7″ / 73kg) & I started with 14/16 for most exercises at first, but now warm up with a 20 and use everything up to a 36 for something or other.
You can always chuck in some variations instead of moving up weights though – on a good day I can strip press a 28 but if you press the ‘bell upside down it requires a hell of a lot more grip strength and I need a 20 instead…
I’m guff at the Turkish get up though