I have a 40LM. You usually update the maps every 3 months. As long as you own the unit and it is servicable (working) there is no limit, but remember the lifetime applies to that unit only. My last update went terrible but after several tries it eventually updated.
It's advertised with three hours of life; however, if it's plugged into my cigarette lighter, won't it continue until I shut off my engine no matter how many miles I go?
It will continue for 3 hrs. On a fully charged battery unplugged. If plugged in to cig lighter then continuous use until car battery is dead then three hrs
What is the maximum storage capacity on a miniSD can this device recognize? Also, do I have to look for a certain speed of card (will a 4 will be enough?)?
The size of the card depends on the amount of maps you want to add, for a large region like Europe, a 4 GB card would be enough. Most any card should work with the device.
Yes, the nuvi 40LM can be set to avoid highways and toll roads. The following driving conditions can be set to be avoided: -U-Turns -Highways -Toll Roads -Ferries -Carpool Lanes -Unpaved Roads
Sorry, but you will have to ask the manufacturer of Garmin for that answer. I have traveled through different states using my Garmin and have not had any problems with it. I am glad I bought it. It sure beats reading maps.