Sorry if this comes off as critical but it's something I feel a need to ask...
Do you feel you have maintained a healthy relationship with your wife?
I know that your secondary relationships are important to you as is being free to express yourself as poly-amorous, I completely respect those two points, but you seem to have allowed your partner's undesirable behaviour and (dare I say) mistreatment of you to sour your feelings toward her.
When I first came here (and I am a self admitted newbie!) I was bombarded with the message: to practice successful polyamory, coming from a state of monogamy in a relationship, you have to have a strong relationship and go at the pace of the person who is struggling the most.
That person would be your wife, it would seem.
How much poly is enough for me?
I think you might be asking the wrong question.
My partner said that he would be willing to try poly on the condition that we had a girlfriend (unicorn, to put it quickly) that we shared and that I only saw with him present, at least to begin with.
That was not what I wanted. I tried to go along with the concept as a compromise but then I found out he didn't actually want it either - he had no interest in any other woman; it was just more bearable (read: less painful) than having me have another partner without his presence or involvement.
Then I realised: why would we both go after something neither of us wanted? It made no sense.
You said your partner agreed to open the relationship but couldn't handle you being hurt by a secondary partner. It sounds like that might have been as unexpected a reaction to her as it was to you. Has she come to terms with it? If she's still struggling and trying to restrict you then it wouldn't seem she has, or perhaps other issues have come up, and may need some extra support (you don't seem to have much to spare so another source might be a good option at this point).
I've never practised polyamory, you will know a lot more about that side of things than I will, so I'm just speaking from the perspective of a poly partner of a mono who has grown used to/expected exclusivity to continue. I know it's tricky when you've got secondaries you're already well involved with, I have no idea what to do about your situation, please understand that I make no such claim and hope I haven't offended you or made any assumptions.
As someone else said it looks like you might have already made up your mind and are looking for confirmation that it is the right thing to do. There is no right or wrong, just choices, and no matter what I or anyone else says it's a choice which belongs to you. In your relationship with your wife this seems like a relatively short (if unbearably difficult) situation compared to the happiness you've shared.
I'm stubborn, I know, but I do recognise that everyone has a breaking point. If you don't feel you have give her what she needs and your needs in the relationship are not being met then perhaps it is time to consider other options than continuing to stay married to her. The relationship will always remain, you have children together, the marriage may end or simply change. I like to look for options with lateral thinking, myself.
Rather than "how much (or little?) poly can I handle?" I would ask myself: "Can I cultivate enough patience, love, understanding and tolerance to make this functional? Am I willing/prepared to?" Life (and love) isn't fair but it's worth it.