I do peds and we are a different world from adult m/s but...here goes.
as far as mixing the meds, it depends. Where I used to work my kids got an ave of 6-10 meds with each pass and they were not unit dose. For that, we mixed it all together. Where I am now, we have unit dose meds and i like it sooooooooooooooooo much better. but thats a side note
As far as how meds are given, gravity vs. pushed, we were supposed to do gravity, but for various reasons ended up pushing (slowly) alot of times. also, you can push a little and then take the plunger out to do it by gravity, breaks up any little clogs that would be an issue otherwise.
For pushing the water flush and/or meds (or not) again, it depends on the patient.
I worked at a special needs camp in college, we were told to treat the tube like a fork. Dont push anything faster than you would want it squirted in your mouth.
Hope that helps a bit.