You should not use only one event sheet, it will not help when you need more organisation, also if you really think you will go into performance issues, do it this way:
First make a working prototype at a smaller scale, just working, do not think about optimising yet
Then try to organise it well, so you can modify the needed part easily, read them quickly, and know where everything is
Then see if there are redundancy of actions or conditions (you should not have to recheck the value of something twice inside the all event system, you can if that helps you organise it.)
Then see if there are checks or actions that are done in case where it does not matter (exemple, checking if an the player is alive constantly is not needed, just check that when needed, same goes for updating the hud or other things.), if you do not find them all, it is not a problem at all, it is just to make the events of the prototype easy to read, and to write, yet performant enough.
Do performances measurement, see if you need every element of the game to exist (pretty sure you don t need every thing to exist everywhere on the map at everytime), so if there is a problem, try to deactivate behavior or to destroy uneeded object, keep in mind that when you are not targetting old mobiles, performances are pretty good in C2 so don t go into try to optimise every event and go into micro optimisation, not only it takes time for absolutelly nothing and makes everything harder to read, but also it won t help you learn how to design correctly your game, try to see what is needed and when it is needed, so you can make the device have less calculations to do.
Tl;dr : test early, see if it is working, organize, see if it can be optimised by not checking useless things, do not try to optimise every single event you make, learn to see what could cause a performance drop in which case, so you don t fall into the trap a lot of people fall into: "optimising everything, except what needs to be optimised"
And remember, working code is your first priority, then organisation, then flexibilty, then performances adjustement, if you have a optimised code that is unreadeable nor flexible, you are going to have a worse time that if you have a code that is clean but needs performances adjustement.