NEED HELP

1. Will reducing the size of the Meshes (All meshes, i.e., Buildings including the players and characters) optimize the game and rendering time? Even if the textures are kept same?

2. Is there an alternative for Cubes? Because Spawning about 1k cubes at a time badly affects the fps in my laptop.

3. Can I use unity online multiplayer for free to build a game and use it just to play witth friends? I won't publish that game on any website.
=> If yes, how many max players can play that game at a time (in Different Lobbies) and (in Same Lobby).

 

1. Yes. Fewer verts/faces is better.
2. Yes, but you should be more specific. Imagine a giant cube made up of 1000 smaller cubes. Those 1000 small cubes could be replaced by a single large one. I'd be surprised to find a situation where there wasn't a better approach than spawning 1000 cubes.
3. Yes, but Unity is currently in the process of switching over to a new multi-player approach. But I think UNet should continue to work for a while, and you can always use it on older versions of Unity: https://docs.unity3d.com/Manual/UNet.html I don't think there's a meaningful limit on the number of players

Also, you should edit the title of this thread and make it say something meaningful.