I'll expand a little bit on what David said hwoever fully agree with his comment.
Last year was my first time riding around Northern Thailand and I went through exactly the same thought processes as you. I kind of enjoy the discussion and planning anyway because it adds to the excitement, but in the final analysis, the trip will not go to plan anyway. That often turns out to be a good thing because fate brings us all nice surprises.Anyway, I did take some planned precautions and that formed the base of the trip.
1) I rented a room in a local guest house for the entire month. This had internet, shower, air conditioning, bathroom and bed plus safe storage of he bike overnight. The rate was so reasonable it would be stupid to not do it. This became my base and the landlady became a friend and adviser on things 'Thai'. If I went out for a few days riding, the stuff I didn't need just stayed there waiting for me.
2) I took a decent first aid kit of likely medication. Things for stomach upsets, prednisone as I tend to get chest infections) eye bath, burn creme, sting creme, plasters and suchlike. Small package but gave me the comfort that I could deal with minor stuff.
3) I got a Thai sim card as soon as I arrived and had one or two local guys numbers in case I needed advice.
4) I trawled through this site and looked for good trips to do along with decent places to eat and sleep. Again, in the ifnal analyss I rarely stayed or ate at them because fate found me somewhere else however I had the comfort of knowing what was in the region should i need it.
5) I made a concious choice to not ride at night (well not in the dark really.) Days started early for me as I like early mornings but I aimed to find somewhere to stay no later than abour 5 pm (I went in June so that was about 1.5 - 2 hrs before dark)
6) Whilst I worried about running out of petrol in the beginning it was never to be a problem. There is always petrol available if you keep a check on mileage and use. If in the rural area and you see a chance to fill up, do so even if only half empty.
Then, go with the flow. In my experience, thais are amongst the most accomodating people in the world and you will always find help, adviceand somewhere to stay. Don't book ahead on routes unless it is likely to be overbooked due to some celebration or somehting like that. That will tie you down. Have your base somewhere and go from there. I promise you, you will not be disappointed and it will all gell together.
I am going back 2nd June for a month and this post now has me dribbling with anticipation
Good luck with you planning, enjoy it all