24" works well for me, with ~30" spacing between plants.
For constructing the cages it helps to have two people, but cinder blocks work as well - just be real careful so it doesn’t spring back on you. If you buy the 100’ roll like I did, the cages are pre shaped for you when you cut them off the roll. For cutting I would recommend an angle grinder with a cutting wheel, using bolt cutters leaves razor sharp points. Finally, I just ziptie the ends together and then do my final shaping on the ground - the cages are pretty light.
@bleedingdirt my bad, 5’ is the correct height. The 150’ roll goes a lot faster than you think. I made 4 cages and a few melon / cucumbers trellises and used up almost half the roll. Sold the rest on Craigslist for a slight discount- it went pretty quick. If you go the bolt cutter route, definitely hit the cut ends with a file to dull them.
I just planted my tomatoes, this is what it looks like:
