Re: Handheld GPS differences
I've got a Garmin 78 with the Garmin charts mounted in the cabin on a swinging mount so it swings out to be visible from the cockpit. This is a nice overall setup. I think it's especially important to have it wired into boat power so I can use it all the time. This has been a new addition this season and it's been great.
For route planning I use the iPhone with navionics.
Though I agree with a comment earlier that a larger chart plotter isn't much more in price. The question is whether you have a good place to mount it.