Hi Jamiess,
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I'd definitely make a page. I made my male FB page 2 years ago at the insistence of my sisters. I still don't spend much time on it, or really comment on anything because it's just not me. I don't feel free to be myself there. Aside from family, the only other people on it are a couple of coworkers that happened to find it, and friends I used to know 15-20 years ago. The only picture I have on it is a purposely jumbled puzzle-style one (mostly because the people I knew 15-20 years ago would definitely notice the more recent changes that family and everyone else is oblivious to.)
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A year ago when i started going out and meeting other people as Kay, I started my real FB page.
That's really the only one I do much interaction on or post on. It helps to stay in touch with people that you meet. To me, that's the FB page my real friends are on.

The page for people who know the real me.

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Since you already have one, it sounds like the issue is finding people to friend. Do you ever go out to nearby trans social/support groups, or a nearby LGBT organization? To keep things safe, I limit myself to people I know IRL, or people I know from Susan's.
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As far as safety: If you're not out yet, like me, I'd be careful. Put an avatar up that isn't your real picture if you use a lot of apps (I used a cartoon character). (I started using my own picture last Summer...with no issues yet) Set all your privacy settings to high, so that people have trouble searching for you. (even if I search for "Kay Donohue" in my city, I can't bring it up from my other account. That way the only people that can find you are those that you want finding you. Use a different surname. I keep the two very separate, just as I keep those parts of my life separate at the moment. (I'm hoping to come out soon though) Auto log-ins that remember passwords and IDs can also be an issue on a shared comp, which you may also need to consider.
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As to your wife, that's a difficult one. You need to follow your heart, but I know having kids can complicate things. From your intro post, it sounds like you've felt this way for a while, so it's not going to go away. Your wife is probably ignoring it, in hopes that it will go away. So the question is whether you want to press the issue, and if you do...how...and how much? Living half a life is no fun for anyone.
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But FB should be a fairly safe avenue to express yourself, as long as you take some precautions.