My 0.2 cents
With respect to multiple instructors. Instructors are not robots so I do not think it is unreasonable to evaluate how things are going after the first few hours. But and this is a big but..... it should IMO be a possible consequence of the real issue which is failure to progress. I have a seen a few circumstances, particularly with new instructors, where it was better for all concerned to bring in an experienced instructor to get a student who is struggling off to a good start. What should never happen IMO is a school who is changing instructors for the booking convienience of the school. I strongly believe that is vital to have no instructor changes for the first flight to solo portion at the very least. However under no circumstances should the type of aircraft change before solo.
With respect to touch and go landings. In a perfect world all landings to full stop would be ideal but it is simply not practicable at many airports. However one can often get stop and go landings which a good comprimise and which help put a definite break between the landing and the takeoff, a particularly valuable feature for the early landing lessons.