Instead of having users having to go through the brush tool set, there are people who would find it more useful to have more option under those. I would keep the current options that are available or seen when you right-click on brush size including being able to copy and paste values. The changes I would add are preset values where you can click on, and it'll change to those value. The same can apply to opacity value.
This has already been discussed to death and the eventual result of those discussions was the quick-settings in the pop-up palette.