Dihydrocodeine is a semi-syntheitic opiod used to treat moderate to moderately severe pain. It's simply a mixture of aspirin, caffeine, and DHC (whatever the exact painkiller is, I don't know). The caffeine is added to counter the dopey effects of the narcotic.
The max dosage is dependent totally on you. Every narcotic effects people differently. The only way to find out how much to take is just to do trial and error with yourself. This isn't a dangerous drug that you are going to damage your body with. You've already tried several pills. You can just add another one or two to that.
I'm not sure exactly what it is you're asking. People will flame me for this, but you can always mix some alcohol with the pills. I usually do with DHC. Actually, I have like 200 of the pills just sitting around because they aren't that exciting and there is so much better stuff out there. I don't ever mix E with narcotics, but this is a weak one so I'm sure it wouldn't do much harm. Just seems a little pointless to me.