I may not be the best person to discuss slab built pots with.
@mwar15 @sorce @ABCarve would be the potters that work with that method from what I have seen here. What I can say though is that proportions is the key to making a pot. Pots that are not in proportion may be fully functional, but may not be aesthetically pleasing to the eye. Also I suggest you join a pottery studio or at least take some hand building classes to get access to a kiln. The reason I say this is because most all pottery studios will not fire pottery that is not made with clay that is not purchased from their studio.
My critique.......you should provide top, side, and bottom views along with something that can give as a judgement on size. Looking at your pics I have no way to understand the size of the pot unless you provide measurements. Even with measurements I would have to pull out a tape measure or ruler to look at. Simply adding say a pencil in the picture I can immediately understand the size of the pot. I like the design. The length x width seems appropriate, I can't say about the height as there isn't a side view pic. You need to work on your seams. Ensure they are joined properly as seams can open during the firing process. If your clay has grog pay attention when smoothing out the pot especially when using a sponge.
Your drainage holes look excessively large for that size of pot. I would make them smaller and add wire holes near each corner. Since you mentioned these pots will be unglazed everything you leave on the pot will show. So unless you are wanting a specific look always keep that in mind, glaze can help "hide" imperfections. Dry slow to prevent warping and cracks.
What Cone does this clay mature at? Absorption rate? Shrinkage rate?
Poke a hole with a pin tool or long nail, then enlarge the hole with a drill bit to the desired size when the clay is leather hard.