Round 1:
I think I built the A frames 1st, then added the bottom tier of bars at sitting height, followed by the other two tiers. bolts were just done up loosley.
Round 2:
get everything into proper position and tighten bolts.
Round 3: A few weeks later, after actually using synths on the rack, I had got a more exact idea of where I actually wanted the synths to sit and did a final adjustment accordingly.
To move the rack, I could now split it down to the 2 x A frames & 3 x tiers and the positions would be retained, so reassembly would be quick & easy.
Round 4: much later, I made a shelf out of ply wood, which allowed me to put a drum machine on the tier with the shortest keybed synth.