Not sure if it’s ich. The one time I delt with that the spots were all over, but it still might be. Make sure the temp is over 80F and you feed plenty of protein. The increased temp will accelerate the life cycle of the parasite which will make them die out and the increased protein will boost his immune system.
As far as tank mates I would say no. He does not need them and in that small a tank which is plenty for him, a tank mate may get bullied and there really isn’t enough room for it anyway, except a mystery snail or two.