If it's stalling when the engine's cold, apart from the obvious stuff like fluid level and contamination of the clutch plates, it might be worth also checking the piston inside the slave cylinder and the pressure plate on the clutch (when that comes apart) as both are prone to fusing with the pushrod which makes engaging first gear a really crunchy experience.
Just a thought but it looks like the bike is running non standard foot rests. Have you checked for play in the gear linkage mechanism? If there's any slop in the linkage then finding neutral will be really tricky. Generally speaking, Ducati gearboxes are on a par with Japanese stuff so if the clutch is OK (sounds like it is now), you're running the right oil and the gear linkage is tightened up then finding neutral shouldn't be a big issue. If it's a case of there being actual resistance at the gear lever (rather than just dropping straight from first to second) then that might suggest a bent selector fork but I wouldn't panic about that until all the other boxes are ticked! Good luck.
Apparently many people find it finicky …
the monster headers are all 40mm od, if that's what you were going off.
no, they're all 40mm. the ss are smaller.