Getting the fixture profiles installed on the M260 is a good start. Hopefully you chose profiles that used less than 16 DMX channels. If you profiles with a higher number of channels you will need to redo the installation with profiles with 16 or less channels. If you want to keep things simple for now, I'd suggest that you use a low - maybe even the lowest - number of channels for each fixture.
You mentioned 20 fixtures and said you had others. The M260 can control up to 24 fixtures or 24 groups of fixtures. You'll need to decide whether you want to program each fixture separately or if you want all similar fixtures do the same thing whenever they are on. For example, you could set it up so that whenever one Dekker comes on, they both come on and do the same thing.
If you want to keep things simple so you can get up and running in a hurry, I'd suggest that you start out with all like-kind fixtures as a group (that is, they all do the same thing when they come on) and just use the built in programs. You can change this later when you get more up to speed on DMX and light programing.
To do this you have to go into MENU/CHOOSE FIXTURES on the M260. In there you assign a fixtures to any of the 24 buttons on the left. For example, you could make button 1 the button that controls your Dekkers, button 2 the button that controls your Galaxians, etc.
Then you will need to make sure that each of the fixtures is set up in the same number of channel mode as the channel mode of the profile you chose. Find out the number of channels used by your profiles your installed and set the light to use that number of channels [How to do that is in the manual for the fixture].
Then set each of the fixtures to the correct DMX channel. Go to MENU/PATCH FIXTURES on the M260. It will first show you that the channel of for button 1 is channel 1. If you've got button 1 set up to program your Dekkers, set them to channel 1. Turn the wheel and you will see the channel for button 2. If you are using an 8 Channel Mode profile for the Dekkers, then it will say that the channel number of button 2 is 9. Set the channel on the next group of fixtures (your Galaxians?) to channel 9. Keep doing this until all your lights are properly patched to the channel number for the button which controls that group of lights.
Assuming you've daisy chained all your fixtures with dmx cables from the M260 to all the lights, you are now ready to program the M260 to get the lights to do what you want them to do.
Let me know if this doesn't solve your problem.