Things i've yet to get my head around are what the differences are between the chip types ie ws2801, ws2811, LPD8806/6803, TLS3001, TM1809/1803/1804/1812, HL1606,etc
Do they all do the same thing?
Possibly, but they will all do it in different ways. Some will handle just on and off and others will allow you to send brightness information as well. The method of getting the data to the LEDs as well as how often you have to refresh this data will also differ.
Also is the voltage important to brightness i.e 5v,12v and 24v strip?
No if a strip is designed to work at 12V, that is what you give it. Running it at 24V will only damage it. The basic criteria you need is the brightness and you will not get a clue about this from the working voltage.
so i assume i will need to use a dmx to pwm decoder to control these!
You will need a dmx to something but that will not be a PWM signal. A PWM signal will only control the brightness of a strip where all the LEDs are doing the same thing. From what you said this is not the sort of strip you want. You want and individually addressable RGB strip capable of doing different brightness levels.
Unfortunately I do not know any I would recommend but the vast majority of strips are not what you want.