1) Thanks for your responses. I've done some looking around and I've found this:
There is first class bus service from the airport to both the ADO bus station in Cancun and to the one in Playa del Carmen. If you are going to Puerto Morelos, you can arrange being dropped at the appropriate intersection on the way to Playa. To get to the buses, go outside the main building and turn right. Head up past the end of that building and find the appropriate bus for you.
Buses are the cheapest way to get around Cancun and you can get from the Hotel Zone to almost anywhere for only 6.5 pesos (Mexican coins only).
R1 – R2 – R15 – R27 all travel within the Hotel Zone although only half of them go as far as Wet n’ Wild – you need to ask the driver
R2 – R15 go to Walmart and the Market 28 in Downtown Cancun
R1 takes you to Puerto Juarez where you can catch the ferry to Isla Mujeres
R27 take you to Plaza Las Americas
There is also the Bus One (a white bus) which is the only bus with a/c travelling in the Hotel Zone. This costs 11 pesos.
If you want to get a bus to another town or city then you can go to the bus station on Avenida Tulum and get buses to Playa del Carmen, Tulum, Merida, Chetumal and just about anywhere you would like to go in Mexico. The ADO bus service is very comfortable and reliable if you are planning a long trip.
Cancun is very easy to navigate. To the South is the airport, to the North is the city and in between are all the hotels, beaches and bars. Buses head up and down the main thoroughfare (Blvd Kukulcan) constantly and are cheap, but be prepared for a cramped and rough ride. Taxis are plentiful, but a bit expensive.
2) I've also read a lot of reviews and these are the top rated Hostels:
Cancun - stay at Hostel Quetzal, Hostel Meson de Tulum, International Club Hostel or Haina Hostal
Isla Mujeres - stay at Pocna
The time has come to make a choice. Either you choose to be at your desk, on time, everyday, or you choose to travel and see the world.