Here's what I suggest...
Make a copy of your Un-Modded No Mercy folder. Run it with no cheats or settings altered and check that it runs properly with no issues.
If so, add the 3 plugins in the settings. Run and check.
If Ok, add the save file from WWF Legends (WWF No Mercy.fla). Run and check.
If Ok, add the rom from WWF Legends (you will also need to go to File / Refresh ROM List). Run and check.
If Ok, add the textures folder and turn textures on. Run and check.
If Ok, add the cheats file from WWF Legends (project64.cht). Run and check.
See how far it gets. If after each one it doesn't crash, move on to the next.
If you get to the same crash, I don't know what to suggest next.
If ok, you can then start adding all the other settings 1 by 1 and testing until you find the culprit.