Did you ever hook up the car to an oscilloscope? All you did was change parts and hoped that your problem was cured. At least that's what I get from your post. Did you take it to a shop to diagnose the problem. I find it hard to believe that a competent Tech would not be able to identify a miss.
Sorry to hear about your issues but who supposedly did the pre-inspection on this vehicle? Maybe the fixes are simple and maybe they are not. I would take it to a lexus dealership and pay the $130 for a proper diagnosis if the web is no help. Try this forum also to get quick answers to your questions.
https://www.clublexus.com/forums/ls-4th-gen-2007-2017-178/
As long as the bolt pattern is the same they will most likely fit but there is more to wheels fitting besides the bolt pattern. It's best to test for a wheel first if you can.
I have KYB-GR2s and they ride close to stock but not as soft as stock. I recommend getting those. ALL the suspension and steering components need attention on cars this old. If you have the money and are inclined I suggest you get it done.
I would use them since techs always forget to replace them whenever they take the covers off. I also need to buy some since I made the same mistake when trying to take those covers off the wifes car.
Plenty of ppl complain about they way Lexus deals with some of their customers. They are right to tell you that the car is not safe to drive with this airbag issue since there is a chance that it could accidentally discharge or worse not discharge at all in case of an accident. My issue is that they don't have parts available for a 10 year old car. Have you contacted Corporate or have you been dealing with a particular dealership?
Personally I would find a seller with more feedback, this seller does not seem to have any. That's pretty cheap considering how much the OEM parts cost but at this stage in the cars life I would definitely go aftermarket for parts.
Your best bet is to find some decent ones out of a car in the junk yard. I doubt that they are still making seatbelts for your car.
http://www.car-part.com/cgi-bin/search.cgi