I have a current FSA for medical and dependent care reimbursements. How will this impact my ability to join the HSA/HDHP plan?

You will need to spend all your FSA money by December 31, 2020 in order to contribute an HSA.  You do have the option of enrolling in Limited Purpose FSA if you are participating in the HDHP/HSA; however, the Limited Purpose FSA is for vision and dental expenses only.

You will still be able to enroll and participate in the dependent care FSA.