Have you tried using the size slider to change brush size? The three finger gesture is an optional extra for people who's fingers fit (not everyone, I know!). If you open up the tool picker and drag left and right in the size indicator you can change the brush size. This is also covered in the in-app manual (tap the ? button and you'll get help on all the different areas of the app).
Creating a new drawing should just involve tapping the gallery button to leave your current painting, then tapping the + button and selecting New Painting. Because we simulate the way paint interacts with a canvas, you get the option to choose a type of canvas before you start (this changes how the pigment breaks up on the surface when the brush starts to dry out, and how it interacts with the canvas when you're blending and spread lumps too far). Incidentally, this is also why we don't provide opacity control in the iPhone version, we're handling an actual simulated pigment volume and opacity isn't quite as important to our approach as properties such as thinners and brush head loading.
My original designs did actually have smaller tool and colour pod items when the control bar was collapsed but we didn't get a chance to implement them initially, they will probably go in to a future update. In the meantime, both pods will vanish if you paint close to them, then reappear when the stroke is done.
We don't plan to introduce shape tools. ArtRage is a freehand (free-finger I guess) package rather than a drawing package and we prefer to focus on the simulation of the physical medium.
Thanks for the suggestions!