I have only used SEM brand. I can get them as cheaply or cheaper I suppose because of no shipping at my local auto parts plus. They can usually get my colour in a day or 2 from one of their warehouses.
For prep, I would use a good degreaser and maybe soap and water. Not sure if a very mild solvent type cleaner would hurt the plastic, maybe try on the back first. I have used Simple Green as well. Big problem would be with getting all of the armor all off, but it has most likely offgassed itself over the years.
With the SEM, I have and have not used the adhesion promoter, I did not notice a difference and the last couple of pieces I did I did not use it. Doesnt cost but another $14 so may be worth the price for insurance.
After the colour I always use the satin clear coat.
Like ALL paint jobs, prep is the key. Spraying the 'dye' on is easy peasy. Only problem I ever had was doing so in extreme humidity and it clouded up badly, but that shouldnt be an issue this time of year.
