TIm, they come with everything you need for your 383's, for your 550ex on a hot shoe adapter, get the best you can (preferably metal construction). Some of the hot shoes (even in the $35-$45.00 region are very poor) If you were able to get a good strong version, try to get one with the 3.5mm mono plug or modify it to take one. Any & all of the hot shoe adapters I have purchased (4 different ones), the PC connectors have been rubbish.
Velcro is the way to go to mount the transmitter on your camera mounted flash (I mount mine on the side opposite the battery door)
The first thing you need to do to the receivers is to glue a rubber washer over the on/off switch.
Left hand edge of this shot:
You probable should also get a Screw-in type PC cord (FlashZebra)?? from here, if B&H don't have them. Nothing worse than having the one in your camera falling off.
Here is a bit more detail on the washer, I used a seal from the underside of a roofing TEK screw and glued it on with No-more-nails. Good solid glue but you can make a mess. (I'm using the Skyport supplied PC cable here but my 383's are modded for the 3.5mm mono connector (you can just see it) and are also modded for my external 6v SLA battery (permanent mod but still able to use AA's) if I want to go light weight)