I have never been to Atlantic City and can`t help with that part of your question.
However, as regards buyin, there are two possible approaches (I`m assuming here we are talking Pot Limit Omaha High-only):
If playing tight, buy in short (30 to 40 BBs) and play premium hands only.
If playing LAG, buy in for sufficient to cover the largest stack already at the table (or for the maximum permitted, if that is lower).
There are advocates of both methods and, as far as I know, no clear consensus as to which is most profitable.