A bunch of questions about tile mapping, meshes and particle systems !

ny’ello
i am making a 2d game where the world is not randomly generated but still you can edit it, also i want it to be and open world like you can built out as long as you want
but i’m pretty much a beginner and here’s a couple of questions:
1 - do i have to make every block on the screen four vertices in a mesh ? or can adjacent blocks share th same vertices ? i suppse it’s the first option but wouldn’t that be more expensive ?
2 - Should i add all the vertices as i creat the world or should i add and remove them as blocks are placed and removed ?
3 - i’m going to be rendering a bunch of textures, so should i make every block a submesh with it’s own material or is that too expensive ?
4 - I’m planning to use “cool” stuff like lighting and normal maps and i’m planning to add a light to every object plus to some block so like everything is dark but there’s light on the player and on that tree etc. so questions is : First what’s my best bet in ordering ? Should i sort on the Z axis or on sprite layers ? must the light be in front of the meshes or is there 2D ways around it? Also what’s my best bet for rendering ? Is it too expensive to keep enabling and disabling game objects in and outside the camera view ? especially when there’s light on every object
5 - Particle systems…When is it too much ? i just made a fireball that’s three particle systems with a total of 850 particles evrey second…is that too much ? Or is unity designed to deal with it ?
i hope i didn’t make the post too long…answers would be really really appreciated

As far as when the amount of effects you’re using become “too much”, the only real answer is to profile it by going to Window > Profiler. Look at things like CPU usage,graphics and memory usage. “Too much” also depends on things like your target platform (whether its mobile game or PC – high end or low end).

In your first question, if you are taking blocks (either your own gameobjects or a Unity primitive mesh) and placing them next to each other, then yes they will each have their own vertices. In 3D, the way to make this sort of setup share vertices is to generate your own meshes procedurally. Not sure if there is an analog in 2D but I would assume so? Again, whether or not each block having its own vertices would be too “expensive” or just fine just depends on what else you have going on in the scene.

Thanks for your reply !
Well yes actually i’m generating my own procedural mesh, and i don’t think i need a special 2D analog for it, i’m just making a plane. but i’m really a beginner i only know how to generate the thing but don’t know like the “conventions” people follow, so for example in a game like Terraria the world is a mesh (i suppose) so how is it managed, is every block 4 vertices ? is every block a submesh with it’s own texture ?are they continuously “enabled” and “disabled” as you go around?Also when i ask if something is expensive, i’m basically asking is there a cheaper way to do it ?like when i ask about if too many submeshes are expensive maybe someone would show up and tell me there’s maybe a cheaper way to do it or maybe about another method without meshes you know i’m here to learn

Guys please if i could just get an answer for this, it’s all i need and i couldn’t find it anywhere
I want to make my tiles so each one has a texture and a normal map, so maybe a material for each
is it just possible or practical to make every tile in my mesh a submesh ? Or is there another way to do it ?
help would be really really really appreciated
Edit : the mesh is gonna up to 1000 tiles with up to 4000 vertices with 9 meshes loaded at a time, that’s why i’m asking if it’s practical