Do I need to complete the 2018 US Tax Return questionnaire before completing my Q1 2019 1040-ES? Another tax advisor already completed my 2018 US Tax Return.

If your tax advisor has completed your 2018 tax return, why do you need to complete it? Just send in what is already done. You can send in your 1040-es Q1 payment at anytime before or on 4/15. I don't know if there is a penalty for sending it in late. If there is, you can avoid it by sending in double what you owe on the Q2 6/15 payment.