Have you read the manual for YW, YO, or YagiMax. These programs are mostly for novel use only and are far from accurate for design and their manuals tell you that. ARRL indicates the same regarding their on YW design software included with their Antenna Books.
The professional modeling software products are very complicated, and a comprehensive understanding of both input and output is important. If you don't understand the input, you probably would not understand the output using EZnec or some other software. If you just want to learn software you will have to get one of the manuals and start to study a very complicated process.
Do you have a way of producing the hardware and matching parts needed to put your tubing together and get a beam to work with any design? You can buy an antenna kit from Maco for a 4 el yagi that will allow you to move elements around on the boom and you will have all the parts and a workable product if your ideas for change don't work out. At this point in your experience that may be what is really important to you. You can also get their instruction manual and go by that. These manuals are pretty comprehensive and shows you an items list. You can also build a beam with wood, wire, and or tubing if you know how to match the beam when built.
