Phrasty this is exciting stuff for me. I do have to say you have an ambitious time frame to build it!
I built mine this past winter. Was only able to work on it on the weekends, mostly Saturdays. It took me 3 months of Saturdays to finish mine. I built mine as a reverse flow type...works great. I have three thermometers on it. On average, the top rack runs about 20-25 degrees warmer than the bottom.
As far as the tires on the trailer...no worries. I have pneumatic tires on mine very close to the firebox...the sun makes them hotter than the fire.
I do have one bit of advice to pass on though... I used exactly the same hinges on my doors when I started. They are not heavy enough.. I ultimately made my own using some 5/8" round stock and pieces of metal fence post. Not only are they strong, they added to the overall appearance of a heavy smoker!
Feel free to message me if I can help...