Some feedback

Hi, I downloaded your program just for fun, to check it out. I like the idea. Here are some random suggestions that came to my mind while using it:

In the canvas, I'd like the vector stuf to be rendered with anti-alias. Maybe that's too GPU intense or whatever, so Ok. But at least the export render should have the option to render your shapes anti-aliased. Otherwise the program won't be useful for painting, but just for unproffesional explanatory diagrams.
There should be an option to change the precision of the brush. Like, how often to place points as you move the brush. And ideally, an option to make that relative to the "base zoom level".
When exporting, there should be more control over the zoom level and resolution. If it's vector based, there shouldn't be any loss to having the scale be 1.24523 right? Also, you should be able to enter the resolution (like 1080x1920) first, and then select where, and at what scale to crop that from the canvas, when exporting. Also, I think there should be the option to select the export region before exporting, and have a rectangular frame showing your export region. Even though the idea of this program is that you can move and scroll infinitely, that "infinity" is still useful when you're doing something that you want to export. When painting (or doing diagrams or whatever) you often want to try things out outside the canvas because it's quicker than creating a new layer and hiding the lower layers...
It's missing some shortcuts that all image editors have, like a key to snap to 45º angles when rotating, a key to snap to axis when painting (make straight lines), etc. But I'm pretty sure you already have that in your todo list, since this is alpha version and all.
One of the advantages of being vector based, is that you can do some things with brushes that are harder in pixel based. You could have rectangular brushes, oriented to the moving direction of the brush. When you try to make such brush in photoshop, the edges end up all fucked up because it's just pasting rectangles close to each other, and at the outer edge of a curve you can see the triangular edge of each pasted rectangle. In vector-based, you could avoid that by joining those corners linearly. So, I think this kind of brush possibilities should be explored.
I find the brush size change thing when you press shift a bit confusing, because I expected "bigger" to be "up", and "smaller" to be "down", instead of right and left. Maybe it's just because I'm used to Photoshop, tho, but I think most image editors do it like that.
It would be cool if there was the option to "infinitely" zoom out, especially when there's not much stuff.
Moving around the canvas (middle mouse button hold) is laggy. If that's intentional, I suggest not doing that.