If you are open to other options I think I have a good answer for you. I am assuming that you want the polycarbonate tube so that you will be able to see inside the reactor.
If you are willing to use regular white SCH40 PVC like they have at Home Depot, etc. that is used for home irrigation systems, etc. (instead of the ABS pipe) you can get clear SCH40 PVC for the viewing pipe. A good source for that is found here if you can't find it in your area.
The nice thing about the clear PVC (instead of polycarbonate) is that it can be glued with the same PVC glue that you use for the white PVC irrigation pipes. You can even get a clear version of the same glue if you want to hide the visibility of the glue. Doing it this way creates a system where the parts of the reactor are all made out of the exact same plastic so you don't need to worry about trying to mix different types of plastic with each other and getting them to bond.
The clear PVC is cheaper than the polycarbonate as well, and you will only need one glue for your whole reactor. Polycarbonate is very strong, but it is also very soft. It is what CDs and DVDs are made out of, so it scratches very easily (and can quickly become hard to see through), even when compared to clear PVC. Clear PVC is also pressure rated to handle the exact same high water pressure levels the white PVC pipe is, so your reactor will be very strong. ABS is not designed or rated to handle pressure at all, so using the white PVC and clear PVC combination will give you a much stronger reactor when it is finished, and it will end up much cheaper to build.
I would personally never bother with clear PVC for all the elbows and stuff. You are right, it gets expensive quickly that way. I would just use regular white PVC for all the fittings to keep costs down, and white for most of the straight runs of plumbing as well. I would just put a few smaller lengths of clear straight PVC at key points so that I can monitor flows, misting, etc. to help with future troubleshooting.
Like for your setup I would suggest just buying a single 3-5' length of 1" clear PVC and then (if you did decide to put a T for creating the siphon in the pump intake line) reduce the third leg of the T to 1" and then have a little 4" piece of 1" sticking straight up before the vacuum fitting for creating the siphon. That way any air bubbles that are in the intake line end up rising into the third leg of the T (instead of blocking the intake pipe itself) and the whole third leg of the T would have to fill with air before any flow in the main intake line was being blocked at all. You could also then easily see how much air was actually in the intake line at any time as well.
Then put another small section of clear 1" pipe right after the output of the pump so you can make sure there is never any cavitation going on, and then another right after the mazzei as well, so that you can make sure it is not being over driven and cavitating dissolved gases (just in order to keep misting and fogginess in the tank to a minimum), and that's about it. All the rest I would do in regular white PVC. That would be very cheap compared to doing the whole setup in clear while still getting you all the benefits that are gained from using clear PVC.
I would use it immediately right after setup to adjust things and make sure everything is working well, and then I would just let it film over and not bother trying to see through it. Then I would only clean it in the future if I was having an issue that I couldn't easily trace, and in that case I would just open the pipes up and clean them really quick and then observe the water flows to see what is going on.
That's about the biggest bang for the buck you can get out of using clear PVC, because you are right, it will get a film on the inside pretty quickly just like any other type of pipe would.