Pool should NEVER have no water in it, if you must replace the liner at a future date, make sure it gets done when your soil is dry and rock hard, you won't risk any caving then.
As for roofing felt, felt may not be the right material since it retains moisture to some degree with it's porous fibers, maybe rubber roofing membrane, but at the same rate, a good thickness vapor barrier should suffice - thicker than 6 mil though.
The tar is not a bad idea, however, the pool wall is allready coated with about 6 high tech coatings layered for long term protection, if going with the tar, it would be your final barrier against the soil's acidity and plastic shouldn't be necessary anymore.
If the pool co. tells you 2 feet is fine, then try to slope it in such a way that you crown it at the highest point, and get relatively good slopes around each side of the pool, I would also leave the last foot unfilled - about 3 feet out from the pool wall, lay in some 4" Big-O tube (it's perforated plastic drain hose with a silt filter sock wrap) and backfill to grade with 3/4 inch gravel or pea gravel, this will stop weeds and grass from growing next to your pool and provide adequate drainage around the perimeter of your pool so it does not get overly sarurated soil all around it.
I have the septic bed beside my pool, so a hill comes down to directly beside the pool wall - in order to stop water from collecting there, I dug a trench around the pool and laid in the Big-O and backfilled with gravel and it seems to do a great job removing the water that used to collect there after rainfalls.