Hi there Alex, welcome to the forum!
1. It will probably take a couple of hours to reach full charge, but you can use it any time before that with a partial charge.
2. Sure! You can use the laptop while it's charging, no downtime, no waiting.
3. Usually a restore disk is enough, but if you have the means to make a system image, then by all means, do so! A little extra insurance is always a good idea. Another good idea, after you have both means of recovery, is to test the recovery media to make sure it works before you need it down the line.
You have a very nice ThinkPad there...don't let it keep you up all night!