While I have never tried hydroxyzine personally (but I have experience with cyclizine, a very similar medication), from what I gather, anywhere from 25-100mg is a typical dose. 75-100mg hydroxyzine would likely be pretty sedating, but might leave you feeling groggy in the morning (esp. if you have no tolerance to H1 antagonists). do you frequently take any other drugs with anti-histamine properties? Perhaps you should try only 50mg your first time to see how you react to it.
Don't expect too much from this combo though, anti-histamines+ethanol isn't too exciting (it won't miraculously be euphoric à la opioids)... it can be a nice way to mellow out after a long day though.
It can be tricky to balance the effects of both drugs though. It's easy for the alcohol to overpower the feelings from the anti-histamine, or you might just get sleepy from the anti-histamine and go to sleep before you get drunk. I think your best bet is to take a medium-level dose of hydroxyzine, then slowly have a couple drinks over the next hour. You're going for 'buzzed' on the alcohol, not 'drunk' or 'wasted' if that makes any sense to you.
good luck.