>>36546342If you want your team to have an easier time through the gym leaders, elite four, and Team Aqua, you'll want type coverage against Rock, Fighting, Electric, Fire, Normal, Flying, Psychic, Water, Dark, Ghost, Ice, Dragon, and Steel.
You'll need a Water-type for Surf, Dive, and Waterfall. Honestly I wouldn't hold it against you if you picked Mudkip as your HM slave and just unboxed him to get across the ocean. That's what I had to do when I did a solo run. A Fighting-type will get you through a lot of your obstacles, having an advantage against Roxanne, Wattson, Norman, most of Team Aqua's Dark-types, Sidney, Steven and half of Glacia's team. I don't know if I'd recommend Fire since half of the trainers you'll encounter in Hoenn are Swimmers and Sailors with Water-types to throw at you. A Dark-type to take on the twins, Phoebe and Glacia's not a bad idea.
So how about giving yourself a Water, Fighting, Dark, Electric, Flying, and I dunno maybe a Fairy type?