I would suggest a way of implimenting the max-mobs-per-chunk setting or enabling it and setting the limit at 5 thousand or so. Im not sure with your stacker plugin if it counts 1000 stacked entities as 1 entity but i wouldnt think it would. Ive had times where I go afk for a couple hours or so and i come back to a massive amount of blaze that could potentialy lag the server so I have to delete the floor and let them fall in the void to get rid of them instead of killing them because skyblock would possibly lag.
Each stack is counted as one entity. The same applies to stacks of items. Unlikely to lag the server out.
False. I can tell you from experience it drops the server down to 1.0 tps especially with double strike and sweeping edge. I made the mistake of hitting a mob and it lagged me out and I had to drop the rest in the void.
As for the stacks go, that depends on how the server is setup/stacker plugin is setup, but I would highly reccomend max-mobs-per-chunk
All someone really has to do, is sit afk at a blaze farm for 2 days and it infinitly spawns mobs, if they have sweeping edge/ double strike, they can really do some server damage
I also didnt mention, you can also edit the spawner properties, and make it a certain mob limit within a set radius of the spawners