Hose reels come in many sizes, configurations, quality and pressure ratings. Some wind in by hand, others wind by hydraulic or electric power. You can mount them on a wall or a deck. Prices vary a lot, depending on the quality of the high pressure swivel, which allows the hose to be played out or wound in while under pressure.
What size? Figure out which length of hose you use most often and go with that. You can always add a small length with quick connectors on the odd occasion that you need more hose.
Use a single length of hose, sized to your reel. Winding up a multi-length hose with connections will make winding more difficult as well as damage the hoses at the tightly wound connectors. Keeping that in mind, there is some law in nature that says a hose will fail in the middle of the length rather than at the end. This means replacing the entire length if you have a blow-out.