As an owner of a self-installed fiberglass pool, I HIGHLY recommend them - WITH THE PROPER INSTALLATION. From your description, and your pool builder's response regarding gravel/backfill, it does sound like he has plenty of experience and strong opinions (normal for good pool builders). While I personally would prefer clean crushed stone, I don't believe you'll have problems with pea stone. It consolidates well, is permeable (for good drainage), and should not experience too much shifting for your shell to tolerate. I would, however, NEVER allow my pool to be set on or backfilled with sand. The problem with sand is that when it becomes saturated with water, it essentially becomes fluid and "flows" - sometimes out from under your pool.
As for the sump pipe: If your pool is built properly (having a 10-12" thick concrete bond beam poured around the entire perimeter, with the lip of the pool being tied into the beam), then the only time you would NEED to evacuate ground water would be if you intend to drain the pool, which most likely can be avoided all-together. With the bond-beam design, the pool, bond beam and concrete pool deck, all tied together, will never become buoyant as long as there is water in the pool - even if the ground water rose to the top of the pool shell. The sump pipe, then, is used in the rare case that you might have to lower or drain the water from your pool. Personally, I never lower my water level. I live in Indiana, so I do winterize my pool every year, but I do not lower the water level at all for the winter. I ensure that my plumbing is all properly blown out and sealed, and a little anti-freeze for extra insurance. For these reasons, an 8 - 10" sump pipe leading to the bottom of the excavation w/ no pump is standard and sufficient.
We also have an auto-cover and love it. With 2 little ones (4 and 2yrs) and a baby on the way, not to mention the crowds of new "friends" you acquire when you get a pool, there's no possible way that we would feel safe w/ an unattended open pool.
Here's my build thread from our pool installation incase you're interested:
I've embarked on the project of a lifetime... self-installing a fiberglass pool for my family (wife and 2 kids under 3 yrs old) here in southern Indiana. I spent countless hours researching different types, shapes, and manufacturers of all kinds of pools and settled on a 16x40 Aspen by Thursday...
www.troublefreepool.com
The amazing thing about FG pools - even doing the entire build myself, it was finished and in-use within 4 weeks. Since then, not a single issue with the shell, cover, plumbing, or equipment. Maintenance is a breeze, running costs are remarkably low, and I don't worry about my liner being torn
