I think you will find it most helpful to read the Finance page of my website Free Frequent Flyer Miles. There are lots of bank and broker deals there. With a large amount of money there is no reason why you can't do several of them.

Most bank deals have early closing fees. You can avoid them by bringing the account down to the minimum to avoid low balance fees until you can close without a fee.

Most brokerage deals have a closing fee, no matter when you close. Also, they often won't pay your miles until you leave your assets for a period of time, usually 6 months. It is rarely a good idea to leave cash in a brokerage account. Their money market funds usually pay very little compared to the banks listed on my website (especially ING and Virtual Bank).