In Phoenix I will be keeping my Redfoot out this winter in her enclosure with some heating lamps and a heating mat.... Your tort might be too small to stay outside this winter but if the dog house is heated then it might be fine
Just recently noticed an opening in her scute (I think it's called) and lines on the back one, and a smaller one on the other side. Should I be worried or is this just an indent? Sorry for bad quality pictures.
Water at the bottom would be absorbed by the coir, giving extra humidity. I believe it would be just fine straight, no need for spending an outrageous amount of money. The heat ropes would be completely fine. Nothing against coco coir so good luck!