I think your first concern should be the s. It's not easily distinguishable from an r or n like that. Try sloping it forward.

'r' --- look more like a small-cap 'R'.

'v' --- I think you should make it like a regular 'v', like down pointing arrow (excuse my english).

'x' --- I think top left side would be better if rounded.

'z' --- try a regular 'z'.

'?' --- imagine how it looks when put beside an uppercase letter, it needs to be wider.

'c' --- I think top right side would be better if rounded.

's' --- I'm agree with Cerulian.

PS: It's your typeface, and this is just my humble opinion. :D

Thank you for the suggestions. Some of the peculiarities are from the rules I gave myself at the start. All the shapes are made from circles or parts of circles, and vertical and horizontal lines. As a result, there are no diagonals anywhere... which means sloping the s would break the rules... but if keeping with the rules means I have an s that looks like an r, then I have no choice but to break them!

How's this? I think it looks more s-like. I thought sloping it would ruin the linking between letters, but it works out. I updated the specimen to the new s.

mk2: I made the current r the way it is because I had designed one and thought it looked too much like an n:

Maybe the old one (in red) is okay, and I've just been looking at all this too long?

I agree with what you say about the c and the v. I think I'm going to do something like what I did with the s.

I previously attempted to make a regular z, but I couldn't figure out how to squeeze in two horizontals and a diagonal into the space of the x-height, so I made a cursive z. The x was the last letter I made, it was really tricky, for the same reason, but I think I can use it to make a regular z. I'll have to work on that.

There you go. The s updated in the pdf looks different than the s in the little red image; I much prefer the one in the image. I don't really see significant problems with the other characters mentioned, but if you're looking for r alternatives, one possibility would be to eliminate the left vertical stroke altogether. And your current z would be improved by retracting the middle left so it's not as long as the top.

cerulean: Thank you so much for your suggestion for the z. I wasn't too thrilled with it before, but shrinking the center part was exactly what it needed, and now I love it:

I changed the specimen again. Now I'm off to start on the numbers.

I took a break from working on this, but I created numbers, a dollar sign, and took a stab at an eszett: