There are three ways of adding a socket outlet to a ring circuit. The most common is to connect it as a spur, and this can be done in two ways. Alternatively, the ring can be extended.
The best method of adding an extra outlet is to extend the ring. This keeps the entire circuit as a ring, avoids overloading at any particular point and keeps two cables in each socket outlet. It may use more cable, and will probably involve additional work if the cables are chased into the wall.
Perhaps surprisingly, there is no limit to the number of socket outlets on a ring. The main limitations are the floor area served by the ring - less than 100 square metres. Most houses have floor areas much less than this, so with one ring circuit per floor, it is unlikely that this limit will be reached.
There are also limits on the total length of the cable, but the floor area limit is likely to be met first.
Do remember that even with more socket outlets, the maximum total load on the circuit is the same. For a 32A circuit breaker this is 7360 watts.