Your tractor has an open center system. Without getting you into information overload open or closed center system refers to two distinctly different types of hydraulic systems. When adding valves to any system, care must be taken to use the proper style valve. Suffice it to say for now that you have an open center system, and any added valves must be open center as well.
A detent refers to a mechanical or hydraulic device that holds a valve spool in a "stroked" position (a position other than neutral). Some remote valves have detents, others do not. A detented valve will continue moving a cylinder to the end of its stroke when the detent is engaged regardless of whether you hold the lever or release it. A detented valve may not be the best thing for a tractor 'newbie'. A properly functioning detent will not hold a valve spool in the stroked position after the cylinder is at the end of its stroke or if the cylinder stalls because it is overloaded.
Power Beyond is a whole other discussion. A power beyond connection CAN be used to power an implement with its own valving such as a backhoe or logsplitter. A remote valve such as you linked to can serve this function as well, and also power a simple cylinder, which a power beyond connection CANNOT do. If you wish to add versatility to your tractor and keep costs as low as practical, a remote valve kit such as you linked to will work well, along with a bungee cord to hold the valve in a stroked position when you want to power a downstream valve such as a splitter or backhoe.
