what are hoops and travelers for and what are the pros and cons of each?

Hoops are essential for helping the helm back to his feet after falling and general balance while stumbling around the back of the boat.
Also has the added bonus of sometimes(when working ) keeping the boom on the centreline of the boat.

The traveller, whether it be on the hoop or across the boat enables the boom to be centralised (or moved to windward) to assist in pointing to windward. A full length traveller across the boat works very well and playing it through waves is a much easier option than continually easing and sheeting the mainsheet.

The advantage of the hoop with a  traveller is that you can pull your self in and out on the hoop when the boat falls over to windward! The hoop is probably easier to use inland than a traveller but there is a fab bit of Harken kit that is self tacking and means that you can tack with the main cleated and have every chance of not filling up.

Travellers and hoops are really there to allow you to bring the boom close to the centreline without loading the leach up - the mainsheet tension is not vertical - a hoop requires less/no manual intervention - a traveller has to be adjusted with each tack.

Are strops what helms do when they can't get the batten over?

You better believe it!

so can you go directly to windward if you pull it to the windward side

Never sheet it past the centreline.

Why not

Makes things seriously slow!

dur wakey wakey Rhodes it will go backwards!!!

full width traveller means much greater control of mainsail than a hoop,gotta be careful not to oversheet though...