In answer to your questions: yes. I think this is a very sensible upgrade plan, although I think you'll want the GAD-29 as others have noted.
I fly a 430W/G5 combination IFR on a fairly regular basis and I'm very satisfied with it. I'm hardly a complete Garmin fanboy, but I think the G5 is really good gear. And I learned on a 430 so the fact that its user interface is (admittedly) a bit old school doesn't bug me. If you're not already experienced with the 430, you can get up to speed pretty quickly on it using YouTube and various aftermarket pilot's guides.
These threads always lead toward recommendations to spend more $ on newer stuff
. But I think a used 430W remains a very good value and a very good option for your panel upgrade. There are a zillion 430s out there so I don't think you'll be orphaned any time soon. I'm ready to be proven wrong, and promise to revisit this thread in five years.
Now it's my turn to encourage you to spend more $$: if you're undecided I strongly encourage you to get the battery backup option for the G5. It's not that expensive and provides an enormous amount of redundancy. A total no-brainer in my view.