1. I don't know where I read that Gateway is limited to 32GB, but it's very probable that their hardware doesn't support more than 32GB in a MicroSD. GW will still work if you decide to use a 64GB MicroSD, but it you have, for example, 28GB conformed by 7 ROMs, and the eighth is an 8GB ROM, this 8th ROM will be ignored by the system since it surpasses the 32GB limit.
2. What are you asking exactly? You can update via internet to the latest firmware version available. For specific firmwares, you use a game that has bounded the firmware you are looking for; otherwise, it may be possible to use a ROM with GW 1.0 version. Now that I think about this, I don't know if they will get rid of the firmware spoof feature in GW 2.0, I doubt it.
About downgrading, you can't. This is only possible using NAND backups.