Brad, These guys have given you some good ideas. Separate units are nice if you have the cash and the room on your console (you can generally find the room if you use RAM mounts). The most popular setup is the Lowrance X102C and the Lowrance Globalmap 3500C (or 3600C if you want internal antenna). A setup like this will run about $950. Note that an internal antenna should be fine on the console with an open boat.
If you have less room or just prefer the compact nature of a combo unit but still want more screen size, then I would look at the Lowrance LCX-25C which has a 7-inch screen. Although more compact, this setup will cost more than the two separate units (about $175 more).
Finally, the most economical way you could go is the 5-inch combo – the Lowrance LMS-334C with internal GPS antenna, or the Lowrance LMS-332C with external GPS antenna. These two units are the same except the GPS antenna. They both cost a little over $600. All three of the above setups will run Navionics Hotmaps Premium Maps and/or Lowrance Lakemaster Maps . Any of the above setups would work very nicely. It just depends on how much you want to spend and how you prefer to setup your console. Feel free to asks us more questions.