I hope you have a tolerance if taking both together. 30mg morphine equivalates out to around 15-25mg of hydrocodone orally, depending on your tolerance. so really, it is SLIGHTLY weaker, but at the same time stronger especially as stated above. Plugging those morph's will have you nodding out hard compared to some 5 mg hydro's.
Correct me if I am wrong, but it sounds like you have a fairly low tolerance compared to many users out there, as I would not even touch a 5mg hydro, unless they were dirt cheap and CWE'd.
Either way, start slow and increase a little after an hour if need be, no need in praying to the porcelain gods. Not to mention, cut your normal dose of each in half at least maybe 1/3 and 1/2, somewhere in that range.
You can always add more, can't take it out.(not comfortably without charcoal at the hospital anyway, assuming orally ingested)
Also, you said IR ER Morphine... that does not make a lot of sense. If they are ER, you must let them soak in water for around 12 hours (crushed), and it kind of kills the ER and turns it into IR, otherwise you may not notice much of anything with a mild-decent tolerance.