Another vote here for .342" no-turn chambers. All of my F-TR rifle chambers are cut with .342" necks, and using Lapua brass, I have never felt the need to turn them. With proper load development, the limiting factor in terms of precision by far is always me. If you experience unacceptably high ES/SDs that even testing different primers cannot tame, turning necks may be something worth trying. Switching to a different [better] brand of brass may also be a solution in some instances; not all brands of brass are equal. Lapua, Alpha, and Peterson are among those brands of quality favored by F-TR shooters.
In terms of neck diameter, a good starting point would be about .002" neck tension (interference fit), meaning that the measured neck diameter before/after seating bullets differs [expands] by .002". The key is to find the correct size bushing, so ordering two or three different sizes is usually a good idea. With Lapua brass, I have always used a 0.336" bushing, which yields very close to 0.338" loaded neck diameter. However, you might need to try bushing sizes anywhere from about 0.334" to 0.337" or so, depending on the neck thickness of the particular brand of brass you're using. If you're wanting to use a nitrided bushing, I'd suggest starting with steel bushings initially, until you find the size you need as they're much less expensive if you're buying several sizes.
Standard trim length for .308 Win should be 2.005". Most chambers will allow for at least .005" (or more) growth in case length before chambering may become an issue. However, it is not necessary in most cases. Using a 2.005 trim length will get you where you need to be. If any pieces of virgin brass are shorter than 2.005", they will usually grow enough to be trimmed after a couple firings, so you can just leave them alone until they do.
As has been noted above, you can always experiment and tweak factors such as neck tension, turning necks, nitrided bushings, etc., at any time. The same is true with other steps and/or tools in the reloading process. The most important thing for someone just starting out reloading .308 Win for F-TR IMO is to start with the simplest and most basic parameters that have been successfully used by F-TR shooters for many years. That will allow someone to get started with the minimum of effort and expense. Once some level of experience has been gained, the odds are better that adding a new step or piece of equipment to the reloading scheme will be fruitful and justify the added time and expense.