working backwards ... new to filing .. ANY HELP !!!

hi there.  i am a few years behind on filing taxes and my cpa is working on 2017 taxes.   i have completed my 2018 and 2019 taxes myself with turbotax....    should i wait until 2017 is completed before filing 2018??  and then move forward to file 2019??

2) also, if cpa is taking longer than expected, how should i go about taking back over and completing 2017???   is cpa entitled to fees if work is not complete???

 

thanks for your time!!