Are you diving on a charter? The DM will be able to help you with your weight setup. Rule of thumb for wetsuit is 2lbs per mm, but wetsuits vary in buoyancy from manufacturer to manufacturer. If you were using a 3mm in training, and go to a 5mil on your ocean dive, you could try 4lbs extra for the suit, and 5-6 lbs extra for salt water. BCs can vary from neutral, to 2lbs positive, to even 4lbs positive. This will be a bit of an unkown if you don't know what the buoyancy of your last BC was, and the one you will be renting. Generally, as you are still feeling yourself out, getting your buoyancy down, you will be a little heavy on your first few dives. You just don't want to be too heavy.
Without the ability to do a predive buoyancy check, I would rely on the advice of the DM (assuming you are going on a charter with a DM). Depending on the type of dive, the DM might be able to help you get dialed in, in the water.
