I would make an educated guess that there is not... it's a very small museum, not at all your typical venue. It occupies a modest bit of real estate in the Reykjavik city center. I'd say it's far better to store your luggage at your hotel, presuming it's near the city center. And if it's not, then why not?

The city hall no longer has a tourist information centre, all their information is available online. There is no combo ticket for the Settlement Exhibition and the Open Air Museum. There is a city card which is valid for 24, 48 and 72 hours which gives you access to all the city and state run museums, city buses and swimming pools.

for kids

not more than 1 hour

We didn't visit the Settlement Center at Borgarnes, can't comment on that. However, it might be difficult to drive around Reykjavik City as parking is limited and is chargeable (we walked around in the city). Thus, Reykjavik 871 might be a better idea if you happen to visit the Reykjavik City Hall or Reykjavikurtjorn (the lake) or Parliament House (just 1-2 blocks away). Get the Reykjavik City card and you will get to visit the museum for free (and few other museums).

Yes 9am - 6pm daily

It's just the Settlement exhibition. The Sagas is entirely separate but I recall it being a pretty small fee.