1) Your primary stat at 18 (post racial) is probably a good idea. Higher than that and you're made of paper, but yeah. It's not necessary going to kill you to have a 16 (either post racial, or without racial) and, in fact, -1 to hit isn't going to get too much notice from you over your carreer.
Where I think Char-Op mentalities go wrong is in the belief that your -secondary- "must" also be an 18 or even a 16.
Take a Sorcerer, for instance. The difference between 16 and 18 in your primary is decent. You hit more often for a bit more damage. That's multiplicating, meaning that your attack effectiveness is quadratic in relation to your score... it's a function of the ax^2 + bx + c variety.
In your secondary, however, the difference isn't even as close to pronounced. It generally only means a reduction in total damage on a linear scale, but it -doesn't- mean enough of a difference to make a difference in rounds.
Think of it this way. Given a choice between a 18 and a 16 in your secondary, ask yourself how often combats have come down to a single point of damage difference? It doesn't happen enough to justify the claim that an 18 is 'mandatory' in your secondary.
And outside of damage, the benefits from secondaries suffer diminishing returns. Being able to shift 1 square vs 2 squares is a huge difference, but at the top end, being able to shift 7 squares vs 8 squares is not enough of an issue.