Hi
I'm in 2 1/2 years into a part-time PhD and can honestly say just go for it. I said to my wife at the start that the depressing thing is I'll be 50 when i finish it. She said what's the alternative? you'll be 50 and won't have a PhD... wise-words

For practicalities you have to know yourself and know how you work - for me I do nothing for weeks at a time and then binge, doing weekends, nights whatever until I've solved a problem/written a chapter/whatever the current issue is. For other people slow and steady is the way.

part-time is tough as you'd expect but as an anti-dote for everyday corporate life it's a fantastic journey. At the end of the day you are out to prove that you can be a researcher and know all that that implies. if you've worked in Academia for a long time you have a head start