Good choice. If ever there was a vintage computer that was worth replicating, it has to be the SOL-20 and it is a manageable size.
I have been keen on replicating some S-100 boards in the past, such as the Dazzler and some others for vintage computers, but a whole computer, that is really something.
One interesting thing is practically all the IC's are still available and not expensive. Though there is the temptation to replace large gate arrays with FPGA's.
When I do a replica I try to make it exactly as the original, even the shapes of the pcb tracks. It is not to pass it off as the original, but just make it as close as possible. I think of it like "making spare parts" and the main pcb might be one of those parts. And then the parts are interchangeable for the originals. This is one very big advantage. For example if you made the cabinet parts identical (the woodwork, the paint color & texture, metalwork geometry etc), they would be a great source of spares for people with original SOL-20's.
One part I found hard to get for the SOL, but finally found them, are the plastic slides that support the S-100 boards, the ones in mine had cracked. The original SOL cooling fans are still available. It might take a batch of transformers to be wound for the power supply. Though you could use an SMPS, but I find the analog supply part of the charm of the whole thing.