1. Below is what I have made so far, using ExpressPCB. How wide do I need to make the tracks and do I need to make them that wide back to ground? (or is it not an issue on this scale?)
your layout looks nice but is it complete yet?
I see quite a few connections which im guessing you want to make using wires.
Also, just wanted to know what programmer you re using since i saw a 6 pin connector.
As for the thickness of the regular tracks and the ground track you can have a width of around 0.04 or 0.05 inches. That should be fine. I recently finished my 50$ bot pcb. ive posted my layout and some pics too.
check it out. it might help: http://www.societyofrobots.com/robotforum/index.php?topic=8821.0
ive made all my tracks 0.04in wide.
2. Can the ground of two different battery's be linked? Should this be avoided?
Are you talking about using the battery holder and the 9V battery together?
This is from Admins tutorial:
"This is the slightly modified schematic for battery holder users. The blue circles with a red dot in the center represent the 4.8V, while the red only dots represent the 9V battery connection. All this means is that the servos use power from the 4.8V pack (which can supply a lot of power), while the sensitive low power electronics use the regulated voltage from the 9V battery. Remember that all grounds need to be common"
The common ground completes your circuit. So, yes you have to connect the grounds of both your batteries.
Hope this helped