Am looking to do a new churn, and here is my status..

I currently possess
UniversalCard Citi MC from 1995
AMEX PLATINUM March 2011 ( will be cancelling at anniversary)
CITI AA AMEX March 2011 ( will be cancelling at anniversary)
CapOne Visa March 2011
Chase CO MC March 2011 ( will be cancelling at anniversary)
Barclays USAir MC March 2011 ( will be cancelling at anniversary)

So far, this is what I'm thinking... getting four all on the same day.
1. Chase United Explorer 60K deal (it's available on my Mileage Plus page)
2. Chase Southwest 2 free flights (I have a working link)
3. ????
4. ????
Note I also was targeted for the Amex Biz Gold Rewards, 50K if spend 5K within 3 mos, annual fee waived 1st yr, but I don't know if this is good enough or not.

Anyone have any advice on the last two I should do, based on any limits of how many cards from each bank like Chase that I can have, and/or the best possible deals out there? And/or maybe you know of some big offers coming up, too? Thanks a million.