Since your confirmation lists the unit number, I would be very surprised if they change it upon check in. The only downside with being on the SW corner is the sun can be a bit overwhelming in the afternoon on the Lanai, but that is pretty minor IMO.
For restaurants, there are so many to choose from, but I will give you a few of our favorites:
Breakfast: Red Rooster, Petit Soleil
Lunch or more casual (although you can be casually dressed in almost anyplace): Marco Island Brewery, Joey's Pizza, Pinchers (walking distance), Stonewalls (walking distance), The Italian Deli (take-out mostly), Lisa and Guy's Philly Grill (great flatbreads!)
Dinner: Two places on the Isle of Capri (20 min drive) that have great seafood and a SW Florida classic feel are The Capri Fish House (our favorite) and The Pelican Bend (next door). On Marco: CJ's on the Bay, Cocomo's Grill, Snook Inn, The Little Bar (in Goodland), Fin Bistro (walking distance)
Beebe's Ice Cream is a short walk to get a cold treat (my daughter's favorite!)
Also, there is a farmer's market every Wednesday Nov - Apr that is worth going to if you are there during that time. There is also a movie theater within walking distance where they serve you drinks, beer and food.
Of course, there are many more places to try out, but these have been our "go-to" places over the years that we have been vacationing there.
Kurt