For what its worth, the software and hardware appliances are virtually identical, so much so that anything you learn on one applies equally well to the other. Console access, HA, RED, Access Points (assuming you can get hold of them) all function in the same way, and so time spent with a home license on a software appliance is by no means time wasted. About the only difference is that the software appliance doesn't support the LCDs on the 220 and up, and also doesn't provide the extra graphic on the dashboard showing what the device looks like.
Regarding firmware, I had always assumed there was something "special" about installing a firmware update on a hardware appliance compared with installing on a software appliance. I think "firmware" is a bit of a misnomer; there are no chips being flashed here; it's just a software update or reinstall whether you're on a hardware or a software appliance. The main difference with a hardware appliance is, when re-installing from scratch, you just pop the CD in, reboot and wait for it to finish - it's an unattended install since it detects which ASG it's running on, and therefore doesn't have to ask any questions in the way the software appliance install does.
On the subject of memory, I have the 8.100 software appliance running on an old (rev.2 I think) ASG 110/120 which I upgraded to 1GB RAM, and also on a brand new ASG 220 which has 1GB out of the box. For the 110, around 65% RAM usage is normal, even with WAF, SMTP Proxy, HTTP proxy and most other features enabled. On the 220 the memory usage for the same release and configuration is around 70-75%. In both cases performance is great, so while I would probably opt for 2GB if I were installing the software appliance on my own hardware, the ASGs work very well with 1GB RAM even with the latest release. I'm not sure what HA, RED and a few APs would add to the usage, however.
