Been on different benzos for 5 years now. Recently clonzepam and restoril (temazepam) don't work anymore. Could I have developed resistance? Would that explain my extreme insomnia?

Unfortunately. All of the benzodiazepines have problems with tolerance which is what you are experiencing. I would suggesting you to go to your prescribing doctor and request to be tapered off clonazepam and restoril and go to a sleep study to see the root casue. Some non-benzo hypnotics available now are pretty effective as well.
Depends. A lot would depend on the dosage and sequence of medications. Yes, you can develop " tolerance " There is also the possibility that this is not simply a medication issue . There may be important psychological issues that contributing to your insomnia and other symptoms . All this should be discussed with your psychiatrist.
Anxiety. IT is possible but maybe the medicine regimen isn't the right one. I would check some blood work as well. See your doctor asap.