Group Travel to Iceland

The G Adventures listing says "moderate" physical grade for the Iceland Waterfalls and Hot Springs trip but I've found that can mean very different things depending on the trip.

I'm reasonably fit but not a hardcore hiker, I do weekend walks, nothing technical. Are we talking proper mountain terrain with altitude gain or more like scenic strolls between waterfalls?

Also curious if anyone has done this in late September, is the weather still manageable or does it start getting genuinely grim?

Considering the Winter in Iceland trip mainly for the northern lights. But I've heard enough stories of people going specifically for them and coming back disappointed that I want a realistic picture before booking.

What's the actual probability on a 7 day trip in January or February? Is there a night specifically dedicated to lights hunting or is it more opportunistic? And if cloud cover kills it the whole week, is the trip still worth doing without them?