Sorry you are taking all that stuff. The side effects must be unpleasant. (It's my very vague understanding that sometimes lamotrigine increases the side effects of divalproex.) It's good to ask your neurologist about the full D3 regimen. If there is a specific interaction with your current meds that he is concerned about, that is important to know; if he freaks out about the large amounts of d3 just in general, as some doctors do, I think you'll have to make the decision on your own. As far as I know, no one has had bad effects from that much D3, as long as (1) they are taking the full regimen, and (2) they have blood tests to make sure that their D levels don't eventually get too high. You'd want to take the calcium part of the D3 regimen 6-8 hours apart from verapamil (because verap is a calcium channel blocker).
You will probably have to order the mask separately. If your doctor is highly sympathetic and if it's possible in Canada, you might try asking for a demand valve system for your O2. If you want to order a mask now, it's at http://www.clusterheadaches.com/ccp8/index.php?app=ecom&ns=prodshow&ref=clustero2kit
We just had a report from a person having very good results with another approach to using oxygen. If you type the phrase "red neck" (in quotes) into the search bar at the top of the page you will see posts about that method, which doesn't require any fancy equipment.
We have found that it's not necessary to be completely off of verapamil in order for busting to be effective, but I don't think anyone knows what applies at 960 mg/day. Sounds like your doctor is really trying to help you and more or less knows what he's doing (as much as anyone does when treating CH). If you think busting might be something you want to try, I guess you'd have to look at all the meds you're taking, and I'm lost there. I can say that for some people, having a good O2 system, having the D3 regimen kick in, and using energy shots makes it easier to get off the necessary meds enough to try busting. (And it's also not completely unusual that when people stop the triptans, their headaches become less bad, probably because of the rebound effects you have mentioned.)