Don’t even think plastic.
Cheap steel tubing is known as EMT in the Electrician’s world. The number of end fittings made especially for EMT is limited; however, it is standard size tubing, so any fitting for 1" (my guess as optimal) tubing will work.
If you can find the fittings you need in EMT boxes, it will fulfill your dis-assembly requirements - they (the versions made for amateurs) use set screws.
For pieces loaded in tensions, drill a hole through the assembled pieces (GE EVERY UBE AND FITTING DRILLED EXACTLY HE SAME!!!) and slip a 8d nail (with the head up, duh) or a nolt and nut if the pin can’t be vertical.
By now you have spent the money required to hire real lighting trusses (those fittings add up quick and are heavy.
Learn how to weld Al and by a hole-saw jig to notch the ends with the saddles (“fish-mouth”) notches in the ends.
If want to write-off the learning curve, the cost of the equipment and welding rod, you may come out ahead of a pro rental, but it will be close.
Then again, if you were the type for whom welding is easy, you probably wouldn’t be trying to sonstruct a truss in which every member is loaded in compression and only compression (which your off-the-wall “slip sockets for everything” would require.
For a giggle, get prices:
Pro trusses, including delivery, rigging, strike/pack and removal
Call a local weld/fabrication shop and ask for a off-the-top-of-head estimate for what you want.
Something which might work - with the advent of cable, all those massive antenna masts are now eyesores - put an ad in Craigslist offering free removal of TV and HAM radio towers.
Then hire professional riggers to do the work - that is a tricky job, and no place for OJT - the first time you fall through someone’s roof or cause a mast to crush a kid. you’ll regret not asking the local tree-cutter if they’d like to use a recip instead of chain saw
Of course, those guys don’t work cheap, and you should have foreseen this need 20 years ago and scored them when they were still plentiful. Now you have a deadline.