I'd say it's certainly much longer than 10 minutes myself. But honestly, I don't feel like it's that bad. Seriously, folks will walk way farther back and forth inside the ICC than that distance.
As as far as sidewalk quality: Presuming no construction starts up between now and the con, it should be just fine. I'd honestly say that crowding will be a bigger issue for a mobility scooter than the sidewalks itself.
Ali Baba's Cafe is a place my group found two years ago and I have gone back every year since, sometimes multiple times. It is a few blocks away, across from McCormick and Schmick's. It has not been busy when I have been able to make it there, pretty much walk in the door and get your choice of seats.
Yes. Get your badge mailed and you'll avoid the biggest line. The second biggest line isn't actually a line but it's the herd of flesh at the door to the exhibit hall each morning (Saturday being the most insane). Finally exclusive hunting can require some insane lines if you are there to play games you an avoid this. Gencon isn't what it was circa 2005 when you could get a block hotel, register for some events and have fun with your friends you may only see once a year. It's kind of a giant cluster now, but I still go because it's still the best 4 days in gaming.