I agree that it's a very good idea to plan a lot in advance and use the collective wisdom of the community to help you plan your system. I started with a Mini and graduated to a SuperMicro board with a bit more capacity and a much better reliability. So make use of the resource guides (there are several) for recommended builds and I heartily agree that buying used can be a much better deal than importing new gear into Oz.
The use case should drive your decision-making process, especially if you plan to use the system for a while. For example, a simple SOHO installation with just file serving on the menu is a very different hardware requirement than someone editing 4K videos on a server or transcoding 4K via Plex. I overbought on the CPU side, would be $500 richer if I'd bought the D-1508 vs. the D-1537 version of my motherboard. (Plus better performance for SMB and AFP).
Despite the best efforts of the community re: guides and IXsystems, the initial setup is a steep learning curve. There will be plenty of things that will frustrate you because they seem so clear in the manual and then they still don't work when you try them out. Searching the forum here can usually answer questions and if not, the community is very supportive. When I rebuild my server for TrueNAS 12, I hope to nuke my ipconfig 100% and start over, hopefully ending up with a bridged SFP+ port setup.
I agree that IPMI is helpful though in a SOHO setting less so than in a server farm. After all, it's not that hard to head to whatever your "server room" is, hook up a USB keyboard and monitor to achieve many of the same features as IPMI. I leave IPMI disconnected due to security unless I need it. I'd also consider putting the IPMI MAC / IP address into a sandbox where it doesn't get to talk to the internet at all (at the router level).