For one, kuhlis are recommended to have groups, they don't NEED to be in groups. My one kuhli in the 40gB is doing great being alone. Been like that for 8 years and outlived the group. Also, the OP is looking for scavengers, not algae eaters. Merited only eat algae.
I buy my pots at Walmart and such. They range from under a dollar to a few dollars depending on the size. They have to have never had plants in them and they MUST be pure terra cotta without a glaze.
Also, as for the stocking, it should be fine. Kuhlis have a very low bioload and I believe would fit perfectly in that tank. The 1" per gallon isn't really used anymore. There's more that goes into it, such as the bioload. You can have a 4" pleco in a 5g. That would work for the rule of thumb, but the bioload would label the tank as too small. See what I mean? Kuhlis stay pretty small and they have a low bioload. They're excellent scavengers and are extremely fun to watch. I would highly recommend them for your tank. Also, is your divider completely down to the bottom of the tank? Because, if its not, then the kuhlis can dig underneath it. I'm not saying that they will, I'm just saying that they can technically have 10g instead of 5g. lol