High lift blonde vs. Bleaching, and vegetable dyes

I've done LOTS of haircolor in my time, and dealt with almost every situation imaginable with color. But I think this time I need some advice from the professionals! I had a question for those who are experienced in using vegetable dyes (such as Special Effects) and bleaching/lightening hair. I have medium brown (level 3) hair naturally. My ends have the remnants of a past bleaching (to around a level 6 orange color) and on top of that is fading out Special Effects Cherry Bomb. I have about an inch of virgin roots. I want to dye my hair Special Effects Deep Purple, but I'm not sure how far to lift the color for the best result. I'm wondering if a bleach bath on the ends might be enough to lift them light enough and be gentler on the already bleached parts? The roots however I'm not sure how to deal with. If I knew how light I needed to go for the best results with the Deep Purple, then I could formulate a plan. Would a high lift blonde take the roots light enough to put the purple on? Or is it advisable to use bleach? I want the dye to be a true purple and not muddy or with a brown undertone. Will the purple cover orange or gold tones brought out by the lightening, or should I use a toner before using the Special Effects to tone down the brassiness?