These are called scuppers and they allow any water that would other pool on the kayak deck to drain. A kayak equipped with scuppers is referred to as self bailing.
When paddling a small amount of water will 'surge' up through the scupper holes as the kayak moves forwards. If you are out on a calm day and no water is coming over the deck then you may wish to fit the scupper plugs / bungs to stop the water rising through the scupper hole.
The Slayer 13 Propel will happily cruise along at 6kmph. To put this in perspective, if you were paddling a non Propel Slayer (either a 12 or 14.5) you would expect to be moving along at around 5kmph when cruising. The top speed of a propel vs pedal kayak is not so different however. The Slayer 10 is a little slower, thanks to a short waterline and more width. It will happily cruise at 4-5 kmph.
A PFD is a Personal Flotation Device, also called a Buoyancy Aid. A PFD differs to a life jacket and life jackets are generally unsuitable for using in a kayak. A PFD has a shorter torso length so it won't ride up when you have a spraydeck on. Lifejackets will float you on your back, which will make re-entering your kayak or swimming more difficult. A kayaking PFD will also have much more freedom of movement around the arms.
It is easy to keep your car keys safe when you do not have a car alarm or remote entry to worry about. As soon as your car keys have some form of electronic 'brain' it become really important to keep them dry. The two best options are dry boxes and dry cases. It is not recommended to use a dry bag for electronic gear as drybags are not 100% watertight. Aquapac's Keymaster dry case is an ideal choice for keeping valuable electronic keys safe.
And remember to securely attach your keys into your PFD so that they cannot accidentally fall out. Most PFDs have a key clip in a pocket.