Well, let’s break it down. I’m doing this from memory so someone let me know if I missed something.
You have reverse so the front clutch drum works as does the low reverse band. The front drum is coupled to the sun gear and it spins the planetary gear set and drives the output shaft.
You said it’s a manual valve body, turbo action? A&A? I ask because TA doesn’t use a L/R band apply in 1st gear and A&A does. With the TA valve body the car launches on the rear clutch set and the over running clutch so if the O/R clutch took a dump and rolled over you would have no 1st gear.
How about starting the car forward in 2nd, will the car move or load the motor or does it sound the same as 1st gear? 2nd gear will be the K/D band applied to the front drum and the rear clutches applied.
A factory service manual and a gauge kit will help with diagnostics of a hydraulic issue. The fact you see nothing in the pan I wouldn’t think failed planetary because they would dump all kinds of stuff in the pan and sometimes lock the car up so you can’t roll it around.
My .02 worth,