PapaQube
Still evaluating SME, and the possibilties of it benefits for home use.
I have traditionally always had a seperate server for the external world, and one for the internal world. I have seen many posts reassuringly promoting the security of everything in one box, but to be honest this is still a hard pill to swallow. Therefore not sure not sure High Availability is what I want.
Not sure what you are asking here. I think you are confusing the purpose of High Availability.
I have used sme servers for 8 years in server gateway mode without separate firewalls etc, and they have performed admirably. There was only one incident with a buggy web application that was installed & got hacked, but thousands of others got hacked due to the same set of bugs in a well known php app.
The issue is not the security of sme server as it is inherently very secure by default.
The issue is really the security of web applications you install, and unwise or inadvertant changes you make that could affect security. A separate firewall does not stop hackers gaining access via buggy web apps on the server.
sme server will be more than you need for a home server, and will be quite OK to use as a "one box does all" solution. There are thousands of them out there doing exactly that.
High Availability is really a way to allow another LIVE server to automatically take over in the event your main server fails, generally due to hardware failure etc, without interruption to any services.
If you want a reliable home server then install two drives in RAID1 array and ensure you have good backup in place eg using the Affa contrib (which will allow you to quickly bring up a replacement system in 10-20 minutes), or use the built in backup with dar (under test) or the Dar2 contrib.