Behr Venetian Plaster setup

Hi... I'm getting ready to do our kitchen in Behr venetian plaster and have a couple of questions... 1. I've stripped off the old wallpaper that was in there (very tough). As a result, some of the underlying paint, etc has come off creating an uneven finish (drywall). Since I'm plastering over it, I wasn't concerned about the imperfections - but have since read that the wall needs to be patched, sanded and very smooth before application (primed also). Can someone explain why the wall needs to be pristine before I plaster over it? 2. I've not purchased the plaster yet. Does it come in particular colors? or do you create your own? 3. What is the point of holding the trowel at 15-30 deg on the first coat, and 60-90 deg on the second? I assume the different angles cause the plaster to go on differently and create the appropriate 'look'? 4. When applying, should I make X's or random strokes?
Any other advice from those that have been through this is much appreciated!
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