Many times when buying juvies, things like curved spinses or other deformities may not become obviously apparent until the fish is somewhat older.
Even if a breeder is good about culling, that breeder may not see certain things right away either in a spawn of 100 or more.
So one thing you may want consider, is whether of not buying one fish is is going to be the one you really want.
The last time I bought a bag of 10 juvie dovii at an auction, two were not worth keeping (one showed deformed gill plates, one a curved spine as they grew), I ended up culling those two, and the group culled itself down a bit more as time went aong.
I see nothing wrong with starting in a large tank, but I like to have pairs that spawn, so perpetuating any deformities that may become apparent with age, would not be something I consider good genes to pass along.