20k B6 points is better than the standard offer of 10,000, so congrats!
As for pricing, in general, the B6 frequent flyer program is based on cost of the ticket. In general, one point has an equivalent value of $0.01, so 20,000 points is roughly equivalent to a $200 in airfare credit. As such, you may/may not be able to purchase a round trip ticket using just these points.
If you want to stack them, consider getting an additional AMEX charge card, as Membership Reward points are transferable to B6. For instance, the Premier Reward Gold charge card by American Express has a standard sign-up bonus of 25,000 MR points after $1,000 spend in three months. However, some people can qualify for a 50,000 MR point offer via
CreditCards.com (hint, fill in the info, as it isn't saved by your SSN isn't required to see the offers).
Good luck!