That is a lot to discuss but not really any questions. If the question is "Can SQL Server handle this type of environment?" the answer is yes but as always, it depends on a lot, configuration of the hardware, disk subsystem, and of course the application layer. The move you mention to 64 Bit will help a lot as I am sure you aware.
As to the other points it would be good to get some details so that more indepth discussions / questions can be worked through.
David
@SQLTentmaker“He is no fool who gives what he cannot keep to gain that which he cannot lose” - Jim Elliot