If Red Sea boats are new to you, any trip, north or south, will be good. I have been north and south in recent years, and against expectation the better trip was from Sharm el Sheikh to Abu Nuhas and Ras Mohammed (though that might have had something to do with Peter Rowlands and Alex Mustard). Trips from Marsa Alam can be good, but my experience of trips from Hurghada is less positive. The Brothers are a big commitment if the weather is less than perfect: perhaps a second trip when you know what's what?
You'll do more dives than you can cope with (a lot of divers start skipping dives about day 3), so be prepared to shoot a lot of images. As a single photographer you might be subordinate to the group, so see if you can find a boat with another photographer on board: a guide who shoots video can be a real asset, as they have an interest in diving photogenic sites, and know where the animals are. I've found being part of a group hinders macrophotography, but wide-angles can work well. The quiet, shallow sites that some old hands don't bother with can be the places to do close-ups: "Alternatives" in the north, "Zabargad" in the south etc. The deeper and more exposed sites can have quite fierce currents, too.
May is good as the water is warming up, but there might still be a chance of sharks; further south April is better for sharks as the water warms faster.
For really impressive reefs, and a really impressive hassle factor, go all the way to Sudan!
Good luck!