Bear in mind that if the helmet did its job most people would tell you that they did not even hit their head, or did not hit their head that hard. And the thin shells on most helmets now tend to hide any dents in the foam. But if you can see marks on the shell or measure any foam crush at all, replace the helmet.

The condition when stored or the conditions underwhich it was stored. Still, if it was in good tune when stored and the tires will hold air, a quick lube of the chain and all pivot points and you should be ready to ride.
Be aware, your tires may not last long, especially if stored with the weight of the bike on them. If it was not stored in a very low gear, it may not shift well (cables stretch). If stored three or more years the brake pads may be hard and need replacing (I can't recommend it, but I have ridden quite some time with dried up pads on garage sale bikes I've purchased). Any leather seat will need treatment before riding too.

5 Rules of the Road for Motorcycle Riders
1. Ride defensively and don't count on eye contact. ... 2. Don't hide in traffic. ... 3. The bike goes in the direction that your face is pointing. ... 4. In life there is no such thing as "too smooth" ... 5. Rule of Lug nuts/Tonnage - whichever vehicle has the most of either, has ultimate right of way.