Frankfurt's Main Rail Station (and the area around it!)

Is the area around the station explorable for 7 hours?
If you mean if there's something to see and do: yes - basically most major sights are within maximum +/- 20 minutes walking distance from Frankfurt Hbf.

Any advice on the easiest way to get to the station?
From the airport: by S-bahn (suburban railways). From the city: S-bahn or on foot, depending on how far away you are.

Also, is there a place in the station to store our bags while we cavort around?
Yes, there are lockers inside the station.

I've looked around the forum and couldn't find any specific advice on these questions
Google can be very helpful too, don't just rely on TT (especially since the December 2012 debacle) ;-)

Is the area around the station explorable for 7 hours?

Yup

Also, is there a place in the station to store our bags while we cavort around?

Yup. It's very close to the starbucks. Stand in front of platform 12/13, walk straight ahead heading for the exit, and it's on your left opposite the customer service centre. Look for "schließfach" which means lockers.

Any advice on the easiest way to get to the station?

From Frankfurt main airport, use the Frankfurt regionalbahnhof (not the long distance train station) and take the S8 or S9. Buy a ticket before getting on the S-bahn; the ticket machines are multi lingual.

Next to the customer service centre (closer to the main exit), there's an office of Frankfurt's tourist information where you can get information about sights to see and the local transport network.

The area around the station does look somewhat seedy in the evenings, but it's generally safe, just watch out for pickpockets just in case.

there used to be luggage lockers at the 'Hauptwache' stop, too, which is only a couple of stops further on the same S-Bahn-line however more convenient for visiting the city centre (mind you, from the main station it's not that much of a stroll either) - maybe one of the locals can sed a light whether that's still the case?

have a look at this city tour leaflet - no.18 designates the 'Hauptwache' stop

I am quite sure I included a link in my post in #3, I'll give it another go here .