Will the space in datastore ever run out?

This is a good question Gmorcad12345! So to start, let's dive into how 'DataStores' work...

When you create a DataStore, it should look something like this...

local DataStoreService = game:GetService("DataStoreService")
local pointsDataStore = DataStoreService:GetDataStore("Points")

So in this example, we called the DataStoreService, and then we called a DataStore, indexed as Points. From there, we can call write & save data to that DataStore by using the SetAsync and GetAsync functions. Let me show you an example...

local DataStoreService = game:GetService("DataStoreService")
local pointsDataStore = DataStoreService:GetDataStore("Points")

pointsDataStore:SetAsync("papasherms", 10) 
pointsDataStore:GetAsync("papasherms")

When we used the SetAsync function, we set the value 10 to the key papasherms, now I do not recommend using a player's name as the key, cause names change, so I'd recommend using their UserId. Now when we used the GetAsync function, it should return a value of 10, because that is what we set it as.

Now, to answer your questions... Does every single player's data get saved into the same data store or every player has a separate data store called "PointsDataStore"?" ... all the player data gets saved to a 'DataStore', saved under a specific key, remember how I mentioned the players UserId earlier? Onto your next question... do I need to worry about the lack of space in the DataStore? ... to answer this question, no you don't; however, there are limits on what kind of data you can write to a DataStore, so be careful of that.

Here is a link to the Roblox Developer website which can better answer your questions on limits, queuing, etc.