I haven't thrown clay in 36 years, since grade school. However, I've been a moldmaker and machinist, and done a lot of work with concrete. In other words, 'plastic' shaping of materials....just not clay.
IIRC, the clay will shrink quite a bit, 10-25%. I recommend try making a couple samples, and get an idea from that.
Since most vanity sinks use a 1-1/4 inch drain assembly, get a cheap plastic sink drain and do some measurements. Then throw a sample drain section (the very bottom) of the sink, and see how much it shrinks when dry, and then again when fired.
If you look closely, you can see how they do the overflow drain as well; the sink is made up of two pieces, glued together with a bit of slip.
Look at a couple sinks to see what I mean.
Then, you can make up a sink (allowing for shrinkage), fire it up, and go from there.
When the sink is dry but not yet fired, you can rub it onto a flat surface (with sandpaper glued to the flat surface) to get the top completely flat (if placing the sink under-counter). This will make mounting it easier later.
If placing the finished sink on TOP of a counter, cut a piece of ply out so the sink sets on/in it. Glue sandpaper onto the ply, and rub the unfired sink onto it to level out the underside of it's lip, getting it flat.
Have you PRICED hand thrown sinks? YE GODS !!! They are HUGE bucks, $400 and UP.
Maybe consider selling them through local shops, with custom work being a specialty. Different shapes, sizes, colors, etc. Go with bold colors (cobalt blue is incredible, so is peacock blue).
Once you figure out the basics of the dimensions for the drain and etc. you could make some real $$$$. All sinks are the same as far as the drains go, they're all just variations on a theme, design-wise.
Nice thing about clay, it's fairly cheap.
Experiment with shapes and volumes of the sink(s). Look at sinks, find a few designs you like to see how they work for you, and work that into your design(s).
The tool storage is nice, but where do I put the bed?