Oh! Also! Points are earned and redeemed on the advertised fare. SW's advertised fare=base fare+excise tax.
If you combine fare types, (WGA+BS for example) you will earn the points on the excise taxes at the higher multiplier (12x in this case). And for redemption, you must redeem points on the lower multiplier for excise taxes (60x in this case). It's a matter of minute points, but I'm sure it will come into question sooner or later.
Also, 40,000 points can be purchased at a time in one transaction. You are permitted to make multiple transactions (from what I recall).
The opinions expressed here are mine alone and do not reflect those of Southwest Airlines, SW's directors, board or employees.