I had both back in the days, and I liked the design og the A600 best... Is it difficult to put in a larger harddrive ? .. Mine back then was only 40 mb :-)
Compact flash with IDE to compact flash adaptor way to go.
For your tv output I suggest you get the Amigamaniac SVHS adaptor works great and flicker free on LCD TV's.
I'd recommend a 1200 rather than a 600, more expansion opportunities.
Need any help let us know. I also recommend for retro gaming purposes to get WHD Load, a great program and worthy of buying.
I also got alot of Amos stuff still, including all the Amos programming books ever written and the Amos Aussie News letter from issue 2 to 9.
If you want to transfer your AMOS knowledge to PC, I heartily recommend Dark Basic Pro (now free with the advert supported version).
Best of luck with it all!