Instead of carrying a heavy bike lock, find something in a joke shop that will do the trick eg. something that makes a bang when your bike is moved. (This one comes courtesy of Hallam Murray, bike expeditionist who has done a number of similar trips ). When parted from the bike for a long time, leave it with a priest, café, hotel etc.
Think of things that fit 2 purposes eg. bike lights will also do for lighting in the tent
Remember people live where you are going, so you will be able to buy stuff there
Keep it simple eg. do you really need the mobile phone
Use many thin layers of clothing instead of a few thick layers. This gives more flexibility and ultimately more warmth
Don't skimp on quality, but no need to spend a fortune either
Better buy a bike on the basis of it having a good, comfortable frame. You will want to change and upgrade the components yourself
Have a 'To Do' list for each week before you go and highlight the things that must be done and by when. The things which are nice to do, you can do if you have time.
Allow a bit of slack in your plans to change the route. Don't try to plan for everything, as this spoils the freedom you have on a bike and will limit interactions with local people
Get letters from embassies to explain what you are doing, to help you get through customs, roadblocks etc
Register yourself with Iamat to get information on good doctors in each country you plan to visit.
Check out other web sites for health information.
Do a SWOT (Strenghts, Weaknesses, Opportunities, and Threats) of yourself and your trip, so that you know what you are selling
Prepare a short (1 page) promotion document and tailor for each potential sponsor. Be specific about what they are sponsoring eg. piece of equipment, stage etc. and, most importantly, what they will get out of it
Don't give up. There are hundreds of people doing the same thing
Call up all of your mates. You'd be surprised at who they know!