Hi, it's cool seeing people already interested in modding :)
I can already think of a few ways you could do this without me needing to add anything, but based on how your level looks, I would use an ACS script. ACS scripts are how all of Snap's maps do most of the advanced level changing. You can make one for your map by opening the "Script Editor" window in Ultimate Doom Builder.
The "SpawnSpotFacing" function lets you spawn any object at "Map Spot" things. You would place the spot thing, give them tags, then use the function to spawn robots in at all of the tagged spots. The script could repeat the action on a timer using a loop & delay, or happen when you step on a line, or when you activate a switch.
Don't really have room to explain further than that, but here's some resources you could look at to learn!
https://zdoom.org/wiki/A_quick_beginner%27s_guide_to_ACS
https://zdoom.org/wiki/SpawnSpotFacing