On the earning side you get 3 points per dollar of base fare for a Blue or 4/$ for BluePlus. If you book online you get 3 extra per dollar. Since you called in you get either 3 or 4 depending on which fare family you booked.

For redemption, yes you need at least as many points as the award price. And the award prices will vary as the cash price changes. You cannot use points for the taxes/fees.

As for the taxes not lining up perfectly, that can happen on some international itineraries, which it sounds like you are booking. If you share the city pair it may be possible to explain in more detail, but some countries charge awards and cash tickets slightly differently for taxes/fees.