You can buy splitter cables for that kind-of power supply and connector. I recently did so, they were cheap, have got some right here. I got two splitter sets (1 to 4) with both male and female connectors, as well as some breakout connectors with both genders. These connectors are designed with LED strips, CCTV etc. in mind, but obviously can be used for anything compatible.
For now, all I really intend to do with this is to split a 12v supply between an 2x50cm LED strip marquee light and and audio amp, for which 5A is plenty.
For your projects, just estimate how much power each circuit uses, and add it all up. To be on the safe side, is good if the power supply rating (5A) is about double that or more. If power supply still runs hot, add another power supply to split the load.
The connectors in my pic are 5.5*2.1mm.