My first question.
I also plan to have a 15 amp (I will use 12 Ga triple rated THHN) line run from the breaker panel to a single outlet inside of the generator enclosure. I would assume that using the 6 Ga ground that will be tied to the ground inside the house at the panel would be acceptable to ground this circuit? Or would I need to run a seperate ground to meet code?

Second question.
Given that the 15 amp circuit I just described above will be live all of the time, would there be any reason that it would need to be isolated from the 6 Ga wires? I will run it and a dedicated ground through a seperate conduit if needed, but thought I would not be even close to fill capacity on the 2" PVC.

Third question.
I am also running an additional 1" schedule 80 PVC conduit for engine control and battery maintainer wires. Because these wires will all be only 12 VDC and be dedicated to only engine systems and not tied into the 120 VAC wiring, would it also need to meet code as far as color? I ask this because it would be a lot more convienent to purchase a 500' roll of wire to run these circuits instead of 10 50' lengths of wire.

My fourth and final question.
This may not be the appropriate forum, but I am willing to bet someone here knows the answer.
This genset is natural gas fueled. My question pertains the the trace wire I plan to bury along with the 1" CTS PE pipe I am going to run to feed it.
I plan to have 2 "T's" in the pipe. One to run a feed for the potential future use of a natural gas fired heater for a hot tub we have planned on down the road, and a feed for an outdoor kitchen i also have planned down the road.
Do I need to run dedicated lengths of tracer wire from the connection point of the pipe to the termination point of my pipes, I.E., 3 seperate lengths of wire, or is it permuissible (and practical) to have spliced connections to in effect only have 1 wire? Given the cost of quality direct burial splices, it may actualy be cheaper to just run three seperate wires. I have not done the math on that yet.

For those that may wonder, I have been in touch with the utility companies and the local zoning department to determine if I can do the install myself. Basicly as long as I get the appropriate permit and have it inspected, I'm good.

Anyway, thanks for bearing with me and thanks in advance.

Also, the 2" sch80 is pretty absurd. It is not a matter if price. It is a matter of running and terminating it. You'll probably have to reduce down in size at some point any way.
1-1/4" is more than enough.

I know that code here does not require sch80, and my only reason to run 2" was ease of pulling the #6 conductors. If memory serves, the conduit fill calculator I checked specified 1" or 1 1/4" for 4 pieces of #6 and 2 of #12. That would indeed make termination easier. Maybe pulling the #6 through 1" or 1 1/4" won't be that difficult, I do not know. I have never pulled #6 through conduit before.

I have not verified as of yet, but this generator was previously installed localy (same codes apply). I have yet to install the generator itself into the enclosure and reconnect the leads from the generator head.
However, I was under the understanding that the critical thing on the ground is that it is not grounded except to be connected to the ground wire that will run back to the ground bar in the breaker panel? Ditto on the neutral. Am I not understanding something correctly, or am I missing something?

Every panel after the generator disconnect is a sub-panel.