Dear Mr. Bojangles,
I'm not quite sure what you need help on. Your post is a bit confusing. You said that you need help with the design, but then you went on to detail the design that you already had. We need to know your problem statement if we're going to improve the performance of the robot. What is the robot supposed to do? I can tell it needs to drill holes at different heights, but other than that I can't tell what specs you're working with. I'll try to help out based on the information that you gave, but it will only be general advise.
If the scissor lift is going to extend for 10ft, you'll need a heavy/wide base to prevent it from tipping over. The joints in the scissor lift section will need to have tight tolerances so that the whole thing doesn't sway.
Why have tracks and wheels? If you can make your design with wheels, why complicate the design by adding a drive system that only works on a track? On the other hand, do you really need the wheels? If you lay track properly, you only need to worry about how far along the track you are (don't have to worry about keeping track of angle and x-y position). It simplifies a lot if you don't have to worry about turning. Plus, isn't it redundant if the arm up top can rotate 360deg?
I'm really not sure what is going on with your arm. It sounds like the 1st joint (lets call it the shoulder) can rotate the arm 360deg (not sure what plane this is in), and can move up and down (redundant if it's attached to the scissor lift). The rest of this arm is a stiff 90deg elbow (is there a reason for this?) connecting an upper arm and lower arm section, with a fixture at the end (where the wrist would be on a human). The fixture allows a detachable part (the drill section) to fit on in two positions; one rotated 90deg away from the other.
The drill section basically sounds like an automated drill press with an integrated, automated vise. The motors that move the drill on its tracks will need to be controlled in such a way that it doesn't break the drill bit by ramming it into the target material too fast, so you'll probably want a feedback loop (I'm not sure what kind of sensor you would use for this). Make sure you protect this section properly, especially since it's swinging around on a potentially unstable 10ft tower. Keep an emergency shutoff switch clearly visible.
Remember to make the arm and drill sections as light as possible so that they won't tip the robot over. I think that using pipes (as opposed to solid dowels or I-beams) for the arm sections would provide optimal strength while maintaining a low weight.
This sounds like an extremely ambitious project for a beginner, so take your time. You're trying to coordinate a whole lot of movements here (base position, scissor lift height, shoulder joint angle, drill position, vise gripper position), so focus on one thing at a time. I would suggest starting with the base and scissor lift. Make sure it is stable and can handle the arm swinging around up top. Keep in mind that this project could get very expensive. Motors ain't cheap.
In the future, please don't try to ask for help / detail your entire robot in three sentences. It's confusing to people who don't know what the robot is supposed to look like. Maybe add a sketch or CAD drawing of the robot to help us visualize it. Also, breaking down your questions into smaller problems will make it more likely that someone will answer you on the forums.