I did mine this spring after 200 hours. I would suggest getting the Honda manual, I cheaped out and got the pdf version. It's clunky because there's it's not indexable, but if you only use it occasionally it works. I found the honda easier to do then my older Merc/Mariner 90.
A second set of hands when you drop the gear case won't hurt either.
All in all, if you are reasonably mechanically inclined it's a do it yourself project. When you drop the gear case, don't forget the bolt under the fin. Other than that, if the old impeller is missing blades, make sure you get them out. You didn't say how many hours on it, but consider at the same time replacing the two thermostats.