The question is a very good one. But there are so many variables for operating boats because they are all so different and handle differently in seas. All these things come into play: Length, beam, hull weight, engine size, flared bow, deadrise, curved transom, full or modified V, reverse chine, porta jack, trim tabs and many other factors. So, to answer your question: "When driving into waves/against wind, what's the best way to trim so the bow doesn't slap in between waves?"
The answer could be bow up on some boats and bow down on others. Also some can ride better on plane across the top of the wave crest, and others off plane and cutting through the wave is the best ride. There is much more. The answers to your questions is going to be time on the water and experimenting with your boat in different conditions to fiqure out which way your boat runs best. Boat handling under adverse conditions is different for each operator since no two boats are exactly alike in the same sea conditions.
When the water gets rough each hull design reacts differently; in fact even individual boats of the same hull style will behave differently because of factors such as load and trim. I suggest you find another boater who has experience with boats or maybe even your boat. Invite him out on the water to show you different ways to handle and pilot your boat. Just something as small as hull type has a very big effect on how will boat reacts to current. Displacement type hulls with considerable draft are affected by current to a greater extent than shallower draft, lighter, planing type hulls. Water is much denser than air, so a half-knot cross-current may have more effect on a displacement type boat than a stiff 15 to 20 knot wind. Given the same conditions, a planing type hull with a tuna tower could be more affected by wind then by current.
Practice in all conditions with your boat, and in no time you'll have it running to peak performance.
Thank you for sending in your question to The Online Fisherman.
Captain David M Rieumont
The Online Fisherman Inc.