Yes, it is possible to start transplanting in the front and then leave a bald crown. The question is whether this look will be acceptable. Will this look scream you had a HT done because it is an irregular pattern. If your hairline in the back drops to a NW6or 7, the look will be unnatural if there is dense hari in the front. BHT could be an answer to this problem, however it really is in its early stages. Toon early for concrete cosmetically acceptable hair growth in my opinion.
IN regards to your last question, all I can say is "you get what you pay for". HT is a journey that can fill your life up with joy or rip it apart. Make sure you do your research and go to one of the few expert HT doctors around. Cant go wrong with IHTI. Good luck.