Maybe I've been told already, but (did I say but?) 27 days have passed and I believe have almost got the answer.. I think..!
HTTPS=true SSL_CRT_FILE=cert.crt SSL_KEY_FILE=cert.key npm start
My one new question, letsencrypt generated 0000_key-certbot.pem files and 0000_csr-certbot.pem files but, Did letsencrypt in-fact generate a .csr file that I can direct the SSL_CRT_FILE=cert.crt to? If so, where might one desiring novice programmer find the generated letsencrypt .csr file?