Well, you've got the right attitude. Find your fly points, use chain rated at least 3:1 for your weight, and you're doubling up by using safety cable, which should NOT be secured to the same points as the chain because what if the point fails?
At $8/foot, it's not that big of a deal to me, not because I got money oozing out of my pores(I'm broke as hell), but because I think that UNLESS you have a massively high ceiling, you won't need a whole lot of chain.
It's not like when I've seen them doing big shows and it's a 100-foot or 50-foot chain going through the motor. Assuming those are $8/foot, well, mega ouch.
Considering whatever chain they were using and whatever motor they were using, they were flying 8 VDOSC cabs per side off 1 motor and 1 chain because the idiot casino refused to set 2 fly points per side for sound. Constant problems with the angles so we had to put a rope coming down to adjust for the proper angle. It just became an ongoing joke and hassle with them.
I have these folding stands that claim to hold 300 pounds, and what I intend to place on them weighs 150 pounds(2 cabs stacked), but the stand itself is "tested" to withstand 900 pounds of weight. I have no intention of testing that. I will say they did hold the 2 speakers, plus 150 pounds of me at the same time, which is WAY more than I needed. This application can be seen on my web site. Look for the big stack pictures, that's what I'm talking about.
Back to your concern, but let's use numbers I can work with. If I was to hang 2 of my KV2 Audio speakers, and with additional hardware, the 75-pound each cabinets will probably come to still under 200 pounds total flying weight with side bars and flying bracket/mount. I'd expect if I were to use motors, I'd want at least a 500 pound motor, but if I could get one rated at 1000 pounds, I'd be happier. Or rigging points with those ratings. EACH!! This way if any one fails, the rest should be able to take up the load. But this is considering a mobile and/or touring application, which is all stuff you fortunately don't have to deal with.
You definately want to have someone come out and check out where you want to fly the speakers from. Don't assume your ceiling trussing or joists are sufficient for what you now want to do, or whatever structure you are intending to attach to. That's why you want someone to come out. Plus, this is stuff your insurance can not crap in their pants over since you again did due dilligence: You got someone to say that its either OK or you need to have this or that done, plus you had someone qualified to get it done to do it, then it can be inspected and signed off on and everyone's happy except you because it cost you extra money. If you do anything to the structure, you need a permit. Chances are, you're going to need a permit for the work.
One last thing: think maintenance. What if... what if you blow a driver(why aren't you front-ending with a speaker processing rack in front of your amps?) or cleaning or inspection. Anything you put in CAN fail just because stuff happens. Be prepared.
You owe use photos of the before and after. OK?