It's good to be interested in taking responsibility for your own health, but your doc will know if there are any undue risks and won't prescribe you anything dangerous. The reason you are worried about this is because people on Bluelight general abuse drugs and take them to the extreme which you are not doing.
Fioricet contains a barbituate, metoproplol is a betablocker, and promethazine is an antihistamine (which like most have some sedative qualities). That being said you are taking doses within the minimum recommended amount and a professional doctor has evaluated the combination and deemed it safe. Consuming this combo is the equivelent of taking a Gravol before going on a boat ride for seasickness and then having a few drinks. Nothing really to write home about.
If you are worried to the point where you can't function then it may be worthwhile to not take anything else until you speak to your doc (to avoid any undue stressing out about it), but don't let reading about the dangers of injecting huge amounts of opioids while tossing back martinis garnished with benzos hold you back from a treatment plan you and your doc decided on. In fact I would recommend avoiding Bluelight altogether unless you were planning on abusing the meds (or at the very least avoiding certain parts of it).
I don't use drugs and would feel completely safe taking the combination you mentioned. I would be happy to lie down and relax for a bit thanks to the barbituates, would fall asleep quickly thanks to the promethazine, and wouldn't suffer from any panic attacks thanks to the b-blockers.
A winning combination.