My Mku is also just 6.5 months. He started to lift his leg about 3 weeks ago, at first very self-consciously - and a bit shaky. Now it is very nonchalant but he only does it if there is a convenient tree. Out in a field he will still squat. But I have seen him cock his leg on a tall dock (plant) after another boy had done likewise.
He has been clean since we fetched him at 9 weeks apart from a couple of accidents over-night on the kitchen floor during the first week. His breeder had done a superb job on him. My Basenjis all sleep out in front of the Aga - large kitchen range.
Peeing on beds / chairs / sofas is not something I have ever come across. I would imagine it to be something you need to get ahold of and stop rather than just playing wait-and-see. If, as is often the case with peeing, it is attention seeking, don't rise to the bait. Ignore it and change the sheets quietly later when there is no Basenji watching.
But check with the vet for UTI.