20 ounces of hops? thats pretty brave, assuming its a 5gal batch since your only using 6.6 gallons of lme.
id go with 1oz of magnum (or any other 14%+ AA hop) @ 60
then 1-2 oz @ 15 , 10 , 5 , 0
then 2-4 oz dry hopped in the secondary
It all depends on how much bitterness and hop flavor / aroma you want as well as what kinds of flavor / aroma you want. different hops will add different characteristics, so it's up to you to decide what you want to shine through.
do some research on the forums here, I know i as well as some other members have pretty comprehensive posts on hop utilization. then use some brewing software like brewsmith or brewtoad.com and play around with the addition until it looks like something you want.