800xA ver. 6.0.3 hardware and OS
What are the minimum PC HW requirements to install 800xA ver. 6.0.3 as a single node system (combined AS&CS) for engineering purposes?
May we use temporary HP workstation Z230 (Intel Core i7-4790 3.60GHz / 4 Cores / 16384MB / 500GB) for example to run the system?
What Windows OS we can use as minimum for that (not Windows server)?
Later on we will move the system to redundant certified HP servers with Windows Server pre-installed, but need to do the engineering in advance on smaller PC
Hard to tell without details, but I suggest to study System Guide (3BSE014434...).
In opinion you will be fine with suggested HW and Windows 8.1 or 10 Enterprise LTSB version (or even Win 10 Pro) for your Engineering purposes.
Bear in mind though, that if you are planning to engineer DCI/Harmony/Melody/MOD300 Connectivity you should choose Windows Server 2012R2 instead.
This goes for AO, batch, calculation services functionality as well. There are limitations on number of node functionality (max 4) on workstation HW/OS.
Another idea is virtualization?
Realistically, throw 4 cores and 8GB of memory at it and it will run well enough so your hardware spec should be fine. At that point you'll get more performance out of it by using an SSD.
Since this is a development system, rather than buying a new workstation, you would be better off spending the same or less money on e-bay and getting a pre-loved server with multiple processors, memory and "enough" disk space to build 6 or 8 VMware servers.