For sure you want to get him on Thyroid Meds, he is way low. So while that will not help his kidneys, it will help make him feel lots better. By the way 1.4 is Low Normal and that is too low for a Basenji
As far as diet, I would look into maybe cooking for him. I don't like the KD because I believe it is corn based. My Kristii is very allergic to corn, so that would never work for me… so I cook for her. On the blood work, what was his phosphorus? Kristii was very high and we put her on a phosphorus binder (which is a tasteless power that you put on the food for every meal) Also here is a link about kidney problems in dogs with lots and lots of information http://www.dogaware.com/kidney.html
Also I have Kristii on SubQ fluids that I do at home, did your Vet say anything about him being dehydrated? That is one of the top concerns with kidney problems. Also I have her on a Pepcid AC once a day because with Kidney issues one common problem is an upset tummy causing them to not want to eat. And I have her on a B complex (human)
The jury is still out depending on what Vet you talk to about protein in the diet for kidney issues…. and in the end, they need to eat... but I have stuck to a medium protein diet for Kristii (who as 15 in December).