Welcome....
1. 5000 pounders should do the trick, just make sure the hooks on each end are long enough to not "shake" off if ya hit a bump. Some guys like the straps with the quick tabs for well, quicker strapping/unstrapping.
2. Yes, highly recommended, this will keep you boat from sliding hull first into the winching area of your trailer, fiberglass always loses to steel.
3. Outdrive up, try to keep it straight if ya can, really doesn't matter if it moves a bit tho.
4. Make sure your trailer is in the water before launching

I usually back in enough until my stern starts floating free of the boards. Of course this depends on the angle of the ramp and water depth.
Above all else, take you time, don't rush because there might be people waiting or you want to look like a pro. I'm new to trailering too, and I have found that doing it right and safely builds confidence and soon you can do it automatically. Oh, have a helper too....