CFI training schedule
Three days a week of flying and/or meeting with your instructor should be fine. Aside from that time, you still need to spend as much time as possible doing homework, i.e. studying and preparing. Putting in only three days a week out of seven toward the entire effort is not enough. It will be hard to maintain continuity and will take you longer in the long run.
The required flight time will depend very much on how quickly you transition from left seat to right. 350's 8-10 hour estimate seems a bit optimistic. I think that fifteen hours is more realistic. Some CFI courses have twenty hours of flying built in. Usually, hadn and foot coordination transfers pretty well. Landings from the right seat are strange at first. You also should receive some hood work from the right seat so you adjust to the different perspective.
Good luck with your training.