I am an Irish citizen travelling to Chinaat the end of the month for 4 months vacation.. During this time I would like to visit Taiwan also..

1/ Will a double entry visa cover my 4 month stay, including my trip to Taiwan?
2/ I have a return flight booked, will i still need to show the consulate an itenery for my stay?
3/ I am planning on backpacking around an do not want to pre book accomodation for my stay, will I be asked to show accomodation details for mt stay?

Thank you in advance..