Are you wanting durations for individual ratings? Like you said, there are many factors that go into figuring out how long it may take to complete a rating. Here is what I typically see:
Private: 3-6 months
Instrument: 3-6 months
Multi Add On private?: 1 month (Most people will get their multi after the commercial so you do not have to take two separate check rides)
Commercial: This varies depending on what training program you go through and how much time building you need
CFI: 3-6 months
CFII: 1-3 months
MEI: 1-3 months
Definitely keep your job and work on the ratings on the side to save money. Once you get your CFI, then you can look at teaching to build hours. Some schools offer discounted aircraft rates to instructors working on additional certificates. This way you may be able to save some cost on the CFII and MEI. All these certificates and ratings are doable with a full time job, it will just take longer.