Is an upgrade from Lumix G3 viable for a noob photograhper?

Short answer:

Go with the lenses and wait with body upgrade till later.

Long answer:

Ask yourself these questions:

• Is image quality you get from your G3 preventing you from getting images you want?
• Is high ISO performance really an issue? How often do you need to push it?
• Would a proper flash not solve low light performance problem more comprehensively? (for me, a proper flash took my casual/family interior shots to a whole new level)
• Would a new camera allow you to take photos you could otherwise make if you'd spend this money on either of the lenses you are considering?
• Does the new camera have features that your G3 has not, and are any of those features actually helpful in making you more productive and/or your photography better?

And I'm not saying that a better sensor is not a good reason to upgrade. That was a major reason for me upgrading from E-PL1 to E-M10. But that was because I started shooting more and more during night, and even some astrophotography, and it became obvious that the old sensor is not up to the task and was a major hurdle for me.

But your situation seems to be different. First of all, my E-PL1 was in a different league than your G3, and all the differences between E-PL1 and E-M10 made the decision very easy for me. In your case, it might not provide as big of an improvement as you'd expect.

If I were you, I would not be considering G5 and G6 at all. The difference is not all that big. G7 on the other hand, is a considerable improvement in every possible way.