44 year old changing careers and looking for input

I'm a 44 year old Voice Engineer, and I'm looking to make a switch to software development, but I'm not sure how to make the move, or exactly where I want to end up. My current job will be phased out in about 9 months, so I'm thinking this may be a good time to make a change.

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About me:

CCNP (cisco certified network professional) – I've spent the last 13 years working on Collaboration (telephones, video conference, etc).

I've been building websites since 2000, primarily forums and wordpress sites, as well as some more robust projects. I am pretty decent with php, mysql, linux (ubuntu and centos). I've made a couple of voice related php programs that are popular, so I have some experience creating and maintaining software. I enjoy coding, and have spend hundreds of hours (nights / weekends) playing with my pet projects.

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Questions:

1. What language should I focus on? I understand that php is out of favor these days.

2. What could I expect for a salary? I'd hope to be at 6 figures within a few years (not sure if that's unrealistic).

3. Are there any entry level development certifications that would help beef up my resume (I assume that depends on the language I focus on).