Sports and sweating will not hurt your dreads. If you are involved in a water sport where your dreads will get very wet, very often, then you may want to use a swim cap while they are new.

Yes, actually your hair will dread easier because the hair has been damaged, so it will hold knots a lot easier. You can use any method and the dreads will lock up.

There are a couple methods for tightening roots
1. Crocheting- this really shouldn't be used for tightening roots, you should only use it to get rid of loose loops. But what you do is stick the dread through the loop and pull it through; it's kind of like sewing.
2. Clockwise Rubbing- In my opinion this is the best way to tighten roots, what you do is, rub the dread against your scalp in a clockwise motion. It has done wonders for my dreads.

Use the clockwise rubbing method. Rub the dread against your scalp in a clockwise motion.

You should use the crocheting method. Just thread the dread through the loop and pull it through, kind of like sewing.