As far as working this stuff out before you get into BDSM, you don't necessarily have to. You can set the limits on what you do there and be able to feel safe when you try. You might even find that, like many of us, you can use play to work your way through this stuff. There are a lot of subs out there who have gone through abuse, most Doms and Masters have come to realise that it's something they will probably face at some point.

Trust is a hard thing to give, but all you can do is be careful. When you meet a Dom, make sure that you can trust him to pay attention to your limits and your safeword. Also, don't conceal that you were abused, be open with him if you think there's a chance that you could end up playing with him.

Separating your submissive tendencies from the abuse is very simple: if you're truly submissive, certain things will feel good. Abuse would be anythng that didn't feel good and right. My recommendation would be to sit down and decide what it is that you like, what draws you to BDSM. From there, move on to what your boundaries are sex-wise. After that, I go on to listing what parts of the past I want to work through and how you think that could b accomplished.

I hope that helps. My Dom used a lot of different techniques to help me work out my past abuse. You can PM me is you'd like to hear more about them.