I have the Sony 28-75mm f2.8 SAM which, if I understand correctly, is a Tamron 28-75mm f2.8 rebranded as a Sony with a SAM motor added. It is good enough to be my carry around lens (although I sometimes substitute the considerably heavier Minolta 28-135mm f4-4.5).
Both the Sony and the Tamron compare well to the CZ 24-70mm f2.8 at a much lower price and weight, according to this review by Kurt Munger.
(Go to the very bottom of the page for his conclusion and links to reviews of the other lenses). The Tamron is the cheapest and possibly the best buy.
You may find the Sony 75-300 f4.5-5.6 struggles on the A900/A850 quality wise. A much better substitute is the Sony G 70-300mm f4.5-5.6 SSM, if you can afford it.
I have used a 32gb CF on the A900/A850 and I believe a 64gb will also work. However I have come to the conclusion that 4gb or 8gb CF cards are the optimum as if you lose the card or it breaks, 32gb is a lot of photos to lose. All my cards are Sandisk CF, Lexar cards may be as good. Try to use cards that are at least 40MB/s to 45MB/s for maximum performance. In continuous shooting mode the cameras buffer will then be the limiting factor, not the card. I would not use Sony memory Stick PRO Duo cards.