Hello msmame, and welcome to cruise-chat;
sounds like an absolutely wonderful cruise; I have heard nothing but good things about Oceania; I have them on my radar for a future cruise. And Malta is my favorite Mediterranean destination (not that I've been to all of them, by any means).
There is really no way of predicting what any seas will be like at any particular time of year. Some areas have certain storm seasons, but it is really hit and miss. Weather-wise November is a great time to sail the Med.; not as hot and crowded. As it's been said here many times, the seas and weather are something you can't do anything about--so don't be anxious about it.
Have a wonderful cruise.