Thank you for your reply racer-x.
Sorry I wasn't clear, I meant these as two completely separate questions.
The blur was just so I could get the same results now as I did with 2.8. So for example if an old tutorial says Gaussian Blur 25 I want to know what the equivalent number is now in 2.10.
The MyBrush is just I want to set the brush size for stroking a path - I have the feeling I'm missing something obvious there

but I'm always getting the default brush size. No problems with the normal paintbrush tool, just MyBrush.
Many thanks.