I found a painting on the internet that's exactly what I'd like to do. It's a painting by a lady called Sandra Strohschein, called Maci's Sunflower, and it's absolutely yummy!
So I decided to try and copy it, so I would have a better understanding of how to approach this. I didn't quite achieve the same sense of movement, but I think the colours and textures work well. So, this is definitely not over yet!
I used black ink for the centre. I know, I know, you should not use black in watercolours, but I like how it turned out, as I sprinkled it with bits of watercolour pencil (using my favourite bit of sandpaper - I got sandpaper in Dealz at some point, and it doesn't work at all, so I'll have to go to Woodies when I run out!)