Costco Free tire/rotation policy?
Be aware of why companies provide free rotation, etc. It's an opportunity to get your car in the shop and "inspect" for other problems. Most business are relatively honest. However, it's always possible they will try to sell you other repairs you don't really need. If you don't know enough to be sure, get a second opinion before letting them do more work.
Relative to tire rotation - there are many theories. With newer front wheel drive cars and radial tires, most people recommend doing a direct front to rear rotation every 10,000 miles or so. Unless there is something bad with your brake disks or something, you shouldn't need a rebalance when doing this.
I know it sounds logical to put the best tires on the front. It does make sense if you have front wheel drive, especially in snow country, since you need the traction and you get more wear on the front. However, if you are concerned about blowouts, the story is different. A blowout on the rear is much worse than on the front. You can steer to control a flat front tire but a reat tire failure can only be controlled indirectly. You are much more likely to spin or lose control with a rear blowout.
Of course, if your tires are worn enough that you are concerned about a blowout, buy new tires tomorrow.