I can't picture the lockers but after exiting customs you have the option to either exit the airport or go through TSA security and be airside. (Before this you can recheck bags and visit the service counter to request a boarding pass--although there are kiosks there for this too--rebook flights in IROPs, SDC, etc.) If you opt to go through security to be airside, you're in an area where all departing passengers are mixed with domestic arrivals. You can follow exit signs to go back to land side and leave the airport as you wish.

Depending on how much carry on you have and whether there are valuables, you could go through TSA security and visit a SC (F/G is closer) to leave carryon bags there, but F/G doesn't have a cloakroom/luggage storage area, although the C SC still does IIRC (to the right of the reception desks or on your right as you walk back into the lounge from the entry).

To go to MOA, follow the signs to exit the secure airside area. If this doesn't take you down one level (by escalator or stairs), follow signs and go down to baggage claim (by escalator or elevator), then go down another level and follow signs toward the light rail station. You'll pass a DL counter for groups (almost always empty) and then take a small shuttle train about a block in the basement of the airport (also going toward rental car counters and rental cars). Then again walk and go down an additional level or two to the light rail station. Along the way you'll see automatic ticket machines, which take cash or credit cards; the fare is a dollar or two, depending on time of day. Frequency is about every 10-15 minutes, depending also on time of day and day of the week. You want to get onto the light rail train going to the MOA, in the opposite direction from downtown. The signs are clear but it's a long walk from security or the gates to the light rail station. The ride is only a few minutes and the station at MOA is down in the basement, but how to find it to return to the airport isn't as well marked as when you're trying to leave the airport, so allow some time to find your way.

In addition to all the stores, the MOA has an indoor themed amusement park (which recently changed brands), an aquarium, a Radisson Blu hotel, a bunch of movie theaters, lots of restaurants (not much fast food and nothing that I'd consider fine dining, but some interesting places with table service and at least wine/beer that are casual, including some family-type restaurants; most are open all day rather than having specific lunch and dinner hours). At one time there was a PMNW ticket office that kept long hours and had monitors for airport flight status, but that went away with paper tickets. I'm not aware of bars at MOA except as small parts of restaurants, but if there are some, they might be up near the movie theaters on the top level in the area called Broadway IIRC, although the Radisson Blu has an interesting-looking bar as well as a restaurant. MOA also features special events which can be free music and other performances, book signings, etc., with all being family friendly in principle. IIRC there's currently some special Barbie doll museum with a steep admission charge.

Highlights include Nordstrom's, Macy's, some big sports apparel/equipment stores, and many familiar brands like Armani Exchange. Unless you're energetic and have lots of time, you probably won't want to walk past every store at the MOA, so plot your path on the floor plan at an information kiosk before starting to wander around aimlessly. There's a MOA store that sells a coupon book and MOA souvenirs, but I don't think the coupon book is worth the price unless your purchases will fit some particular pattern to use the discounts well. You can also find several stores that have Minnesota souvenirs, but this stuff can be found at the airport too.