Initial Training
What you are really proposing to do is finish your initial training. Although I'm not an accountant, I can tell you, sadly, that none of this is tax deductable. The IRS won't let you deduct the cost of training which qualifies you for a new job. You are talking about finishing your basic ratings, those which would qualify you for a different job. Just getting your Commercial and CFI aren't enough. The CFI-I and MEI fall under that classification. Even if you can go to work with just your CFI, the IRS is likely to look askance at your deductions. Moreover, not too many places will hire a single-engine pilot with just a CFI.
Now, expenses that you incur after you get that first aviation job to keep you employed would be tax deductable , e.g., Jepps, job hunting costs including travel, resumes, etc., uniforms, type ratings.
Finishing your ratings will depend a lot on you and the time you can put in. If you can train full-time, you could go to any of the well-known 141 schools and they can design a program under Part 61 to finish you up. You could do it Part 61 at your home airport. You might be able to do it in six to eight weeks. I gather that you haven't taken the writtens yet, so studying for those will take some time. Or else, you can go to a weekend school. You'll need to take writtens for Commercial, CFI, FOI and CFI-I. Along the way, it wouldn't hurt if you took the BGI and IGI writtens and get your ground instructor certificate. The writtens are similar to the CFI and CFI-I.
Hope that helps. Good luck with your training.