This question is very hard to answer without more about your goals (and what discipline you're thinking of) for getting a Ph.D. Ph.D.'s are essentially vocational training for entering academia. If you're really passionate about your subject and think a Ph.D. program is the only way to immerse yourself in it to the depth you want, that's legitimate, but then working full time outside your discipline, will make that pretty difficult. You might want to think about whether there are ways of accomplishing what you want to without something that requires the commitment of a Ph.D. program. The fact that you write "advanced coursework" is an enormous red flag: the point of a Ph.D. is not coursework, and in some disciplines there is very little of it. The point of a Ph.D. is to do research, and that's much harder if you're not embedded day-to-day in a community of other people with the same goals (physical proximity may sound quaint in this day and age, but there's an enormous drop-off in knowledge transfer between different floors of the same building).
I don't like being so negative, but honestly in most disciplines, there are too many Ph.D.s and unless you go to the most prestigious schools, and build a very strong network in your discipline, there's a decent chance it will worsen rather than improve your employment prospects. Ph.D.'s have a specific purpose, and at least your question doesn't make it sound like you've really homed in on how that will serve you well.
