I am with Jim in that I would encourage you to get to know the WSM as it's designed and sold. I will go so far as to say that you should cook with it for six months before you commit to any modifications. And I would use water in the pan for low & slow cooks of 225-275*F and an empty water pan for cooks above 275*F. Water is an insurance policy that helps you control temp, and despite protestations about cleanup, water is used by professionals in many pits to create a moist cooking environment that promotes a better smoke ring and augments any spritzing you do of the meat during cooking.
There are a lot of people who criticize the access door because it's stamped out of aluminum while the rest of the cooker is this substantial porcelain coated enamel steel. The reality is the aluminum door can be tweaked to improve the fit, if needed, and while there are some folks that really like the CB stainless steel door and especially the latching mechanism, there are others who buy it and find that it doesn't fit that well, either.
If you intend to do a lot of overnight cooking, you may gravitate toward a temp controller. I've been at this for 23 years and I still don't use one regularly. I use an alarm thermometer to let me know if my pit temp is rising or falling outside of a set range, and only then do I have to get up and take action. My WSM will run stable for at least 6 hours so I can get some sleep.
Casters? Depends on how much you need to move your cooker around; consider a
rolling platform. Handles for middle section? Useful, but again I've gone 23 years without them.
I'd also suggest starting with a good quality charcoal briquet and using it again and again as you get to know your cooker. You can explore other brands and other forms like lump later.
Good luck, keep us informed of your progress.