As it relates to tire management, you've asked several good questions, but the answers are somewhat of a preference to the driver and dependent upon the track, so the answers may vary..
I'll list a few of my preferences..
The starting "pre-cone or camber" to me is simply a way to get the tires as close to a "pre" race run-in, which eliminates several laps of warm-up before the tires "come-in".. Therefore the degree of pre-coning or camber, is based to some degree on what my car comes off the track at... I typically will run a 5 minute practice and then set the cone angle of the cutter close to what the tires came off the track after the practice. Might be 0.5, 1.0 or 1.5 depending on the track or set-up of the chassis. If the tire comes off the track at 1.0 degree of run-in camber, then I set the tire truer up to "replicate" the run-in angle on a new set, in an attempt to shorten the time it takes for the tires "come in"..
The tire size is also dependent on several variables, largely based on tire wear... When traveling I usually set the car up with the standard suggested size by the manufacture, in my case Serpent 960 (74mm Rear, and 68mm Front). The 6mm split is roughly a 2% overdrive, however, the size allows me to practice and begin adjusting the chassis set-up with a medium sized tire (not the smallest and not the largest possible).. After a few tanks of practice I'll re-measure the tires to determine the amount of tire wear.. This is important to me based on the length of time the mains will be run (back to this in a moment), if your parking lot bashing, start with the tires out of the box (big), get all the use of the foam you can.. If your qualifying, smaller tires is usually the fastest (lower car or CG, more traction and lower gear ratio/roll-out, can be quicker)..
However, for the mains, you'll need to understand how much tire wear you expect to see during your race.. For example, a 30 minute main.. If during your 5 minute practice sessions you notice 0.5mm tire wear, then it's possible you could see as much as 3mm of tire wear during your main. This will let you know how big or small you can begin your main, with lower usually faster, it will let you know how much ride height you need at the beginning of the main to allow for the 3mm of tire wear at the end of the race without dragging the chassis in the corners or under acceleration. This information will let you know what tire size to begin practicing and tuning your set-up along with your 2-speed which changes shift points based on tire size :-) SO, while your thinking about that, also keep in mind that all 4 tires rarely wear at the same rate, therefore you may account for each tire separately for a 30 minute main... Based on a clockwise track (potentially more right turns), you may have the left tires wear faster than the right tires, and require more "stagger" from left to right at the beginning of the main..
Overall, with the amount of change in handling, shift points, clutch and motor variation due to tire size... I practice with tires close to the size of half the race of the main... So, in our example from above, if I started with 74/68, and calculated 3mm of tire wear for the race, I would practice with roughly 72.5mm rears and 69.5mm fronts (roughly the wear at half the race or 15 minutes). This would allow me to set the cars chassis, clutch, 2-speed and motor tune at the mid-point or optimum run condition... When I start the main, the car won't be perfect, nor when I get closer to the end of the run, but during middle or most of the run, it will be where I practiced/qualified...
I use a truer quite often on the same set.. Typically, my race set is trued from the box for the main today, and then is re-trued for next weekends practice/qualifier set... After practice the next weekend, I bring out a new box and re-true for the main. Then the cycle starts all over again.
I start the main on the ideal size, ever thing else is used for practice/qualifying.
Average life span is entirely dependent on the track surface, traction compound and your driving style.. A local track in the area has worn up to 10mm in a 30 minute main, while the same or other tracks have worn 2mm during the same 30 minute main at differing times.... Tire wear is largely about the track...
Any finish from the cutter will likely be a mute point within 5 minutes of running... From the example above, if you're using 0.5mm of tire wear in 5 minutes... Then the finish really only needs to better than 0.5mm in pitting to be great in 5 minutes :-)
The radius is usually cut with a file, they have several "special" files, or a simple rasp from your hardware store. I'd think sandpaper is fine to use, but it may take a little longer and get clogged faster for 1/8th tires.
Economics and 1/8th scale is a very tough balance. When I began, any old tire or size would do (I really didn't know or could tell the difference), as I got a little faster I began to find speed in the tires, primarily around fine tuning everything else (chassis, clutch, 2-speed and motor).. Using my medium race set (not to big not to small, but good for the size of the middle of the main), it allowed me to "set-up" the car for the sweet spot of the main, and allowed me to tune the other aspects, which helped me gain a 0.01 here or there... After finding a few of those "tenths" it became a "second" faster and so on...