Say I was able to get an IDE sidecar HardDrive for the 500. Shouldn't I be able to plug in one of those IDE to Flash Card adapters and use that to transfer the data back and forth? What considerations would I have to give as far as the data format of the card? Would I need, say, CrossDos on the Amiga?
You could do that, but;
A: The CF card would need to be formatted as an Amiga HDD, as the Amiga cannot read any PC file systems on an IDE bus.
B: Due to the above, you'd need to use WinUAE to move files to & from the CF card, as the PC cannot read Amiga file systems. That & PCs screw up uncompressed Amiga files.
Here is my suggestion. Buy a Zorro slot sidecar & a Buddha card. Then you can have up to four IDE devices at once. I'm thinking a HDD to install your OS on (plus storage space), then add a CD drive to transfer stuff from the PC

PZ.