We tend to DIY our holidays to Thailand about a month before we go due to not knowing when I can get time off till a few weeks before we go. We usually book the long haul flights then decide where we want to go within Thailand and the Far East. Have a look around the various flight websites for whose doing best deals. Direct flights usually work out more expensive then indirect flights via hubs such as the middle east. There's a good choice or airlines you could use - Thai, Eva, Etihad, Qatar, Emirates, BA Qantas etc. You could have a look at the websites of netflights, travelmood, southhall travel among many others.
Once in Thailand travel round about is easy and cheap. There are the low cost carriers such as Air Asia and NokAir should you wish to fly as well as scheduled airlines such as BangkokAir and Thai, long distance buses and trains.
There are plenty of accommodation websites such as asiatravel.com latestays.com agoda.com which will give you a rough idea of cost of properties in the various area you might choose. Can't really help with the backpacker side of things as we tend to stay in the 3 to 5star range of properties.
Chinese New Year falls the middle of Feb so this may limit availibility for the period you are looking at. February is a good time to consider the Andaman coast of Thailand, areas such as Phuket, Krabi, Ko Lanta and Khao Lak may be of interest.