Sorry for the delay. Correct, Shift + Control adds to the selection but I just noticed that we don't have a modifier key to remove from the selection(Probably due to some conflict with UE viewport navigation functionality). It will be added soon.
You can increase the brush size with "B"key, is pretty much like in other hosts. For now the brush size will be the same for the selection brush and the selected brush.
Jeordanis Figuereo (Product Designer. EPHERE Inc.)