I'm in a similar situation...
Making a living in computers is a pretty broad spectrum. One one end, you could be maintaining servers and writing incomprehensible shell scripts. At the other extreme, you might be setting up end-user systems, where noone but you would even know that Linux was involved.
To pick a vocation--particularly if you are phasing out of another career, you have to start with an assessment of what you are good at--and what you most ENJOY doing. For me, it's going to be writing and teaching....YMMV