Total noob here

Old school gonard that has moved over to D&D 5E and getting back into development as a hobby. Question where would be a goof place to start to learn to automate and make a way to upload monsters in bulk for random encounters based off the of 1st edition random encounter tables - thanks in advance

This is an interesting one to me, I play AD&D on Roll20.  What do you mean by "upload monsters"? What would the end result of that look like or do? Not sure if you are asking to upload tokens (images, minis), or you want to put AD&D monster stats into a 5E Character Sheet, or if you want to build a random encounter table (perhaps using Roll20's Rollable Tables)? 

A description of what you want to accomplish, described in generic terms "I want to be able to roll an encounter using my own encounter tables and then be able to use those results to place 5e versions of those monsters into a combat against my players as quickly as possible" would be a good start for us to help with suggestions. BTW, I too pretty much skipped from AD&D1 to 5e with only a handful of interactions with the intervening versions. :D