Hydrocodone has little to no efffect on the serotonin system.. but not all drugs that interact with MDMA do. The problem with opiates and MDMA is that they usually dampen the experience quite a bit.
Once, on the comedown (more like afterglow, really) of a great MDxx dose, I took some hydrocodone to help relax me.. it killed my afterglow, left me with and empty feeling where the euphoria used to be. Was NOT cool, I was pretty pissed haha. So, opiates and MDMA are not a good combination.. I'd recommend you stop taking them about a week before you plan to roll, just to be safe. Save some up and use them the day after, that's when you're really going to want them anyways.
Also, I must say.. you're using opiates rather frequently. Don't let it become habitual, friend... too many heroin addicts got started off just popping some vikes every few days..... soon, that 10mg pill won't be doing much, so you'll take 20mg. Then, vicodin won't do SHIT anymore because of tolerance, and you'll move on to Oxy.. maybe Diludid or Hydromorphone, really it doesn't matter what you're taking. Tolerance will continue to build, and soon the only way to over come it is by sticking these drugs straight in your femoral vein... then shit, believe it or not even that 80mg oxy that cost you $120 and that you shot up straight into your neck isn't getting you high, so you switch to heroin. At that point, it just makes sense.. it's cheaper, more available and you can get higher on it.
Well, now you're a full fledged junkie, just because you didn't want those vicodins to stop working.... I'm not saying this will happen to you exactly, but we've all watch many, many people follow that EXACT path here on Bluelight, and I must urge you to stay away from it.
Good luck.
I'll move this a bit later into the MDMA + Opiates subthread, just so you know.