Considering that originally Donuts are meant to be fried, I feel I may not get same result when I "Toast" them at lower temperature. Hence I feel its better to avoid Donut Premix.
Firstly I am not too experienced in baking/cooking. Secondly in a commercial venture I feel consistent taste is the key to success. Thirdly since I will not be present at the joint at all times, I need to keep it simple for the staff. Hence even if it costs slightly more, I am inclined to use a premix rather than making something from scratch.
Considering that donuts are little denser than cake, I feel its best that I use waffle premix rather than cake premix but the reviewers of donut toaster says they used various cake premix in it and were pretty satisfied. I guess I will have to try it pratically.
BTW thanks for the really helpful links 
