DataStore request was added to queue. If request queue fills, further Try sending fewer requests??

Solution

This is where RequestBudget comes in. If there isn't enough RequestBudget, it will show that warning. To fix that, you will need to wait until there is enough budget.

local function waitForRequestBudget(requestType: Enum.DataStoreRequestType)
	local currentBudget = DataStoreService:GetRequestBudgetForRequestType(requestType)
	while currentBudget < 1 do
		currentBudget = DataStoreService:GetRequestBudgetForRequestType(requestType)
		task.wait(5)
	end
end

Now you can use that function in GetAsync() and SetAsync().

-- House Data --
waitForRequestBudget(Enum.DataStoreRequestType.GetAsync)
local houseData = HouseData:GetAsync(player.UserId) or {}

-- House Saving --
waitForRequestBudget(Enum.DataStoreRequestType.SetAsync)
HouseData:SetAsync(player.UserId, Houses)

Pcall (Protected Call)

I recommend using a pcall() when using an asynchronous function since they can error and break the script. pcall() calls a function and if it errors, it won't affect the script and the error message will just get returned by pcall(). If it didn't error and it was successful, pcall() will return everything returned by the called function.

-- House Data --
waitForRequestBudget(Enum.DataStoreRequestType.GetAsync)

local success, houseData = pcall(function()
	return HouseData:GetAsync(player.UserId)
end)
-- or
local success, houseData = pcall(HouseData.GetAsync, HouseData, player.UserId)

if success == true then -- if successful
	for houseName, houseValue in pairs(HouseData) 
		Houses[houseName].Value = houseValue
	end
else -- if it errors (mostly when player has no data)
	print("Player " .. Player.Name .. " has no data!")
	warn(houseData) -- warns the error message
end

Retries

If you use SetAsync() once, there's a chance it might error, not saving the data. What you can do is retry until data is saved.

-- House Saving --
local success
repeat
	waitForRequestBudget(Enum.DataStoreRequestType.SetAsync)
	success = pcall(HouseData.SetAsync, HouseData player.UserId, Houses)
until success == true

UpdateAsync > SetAsync

UpdateAsync() is safer to use in multi-server attempts than SetAsync(), so you should use it except when using an OrderedDataStore (commonly used in global leaderboards).

-- House Saving --
local success
repeat
	waitForRequestBudget(Enum.DataStoreRequestType.UpdateAsync)
	success = pcall(HouseData.UpdateAsync, HouseData, player.UserId, function()
		return Houses
	end)
until success == true

Final Script

local DataStoreService = game:GetService("DataStoreService")
local MainData = DataStoreService:GetDataStore("MainData")
local HouseData = DataStoreService:GetDataStore("HouseData")

local Players = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local RunService = game:GetService("RunService")

local function waitForRequestBudget(requestType: Enum.DataStoreRequestType)
	local currentBudget = DataStoreService:GetRequestBudgetForRequestType(requestType)
	while currentBudget < 1 do
		currentBudget = DataStoreService:GetRequestBudgetForRequestType(requestType)
		task.wait(5)
	end
end

-- House Data --
function loadHouseData(player: Player?)
	local Plot = Instance.new("StringValue")
	Plot.Name = "Plot"
	Plot.Value = ""
	Plot.Parent = player
	
	local Houses = Instance.new("Folder")
	Houses.Name = "Houses"
	Houses.Parent = player
	
	for i, house in pairs(ReplicatedStorage.Houses:GetChildren()) do
		local newValue = Instance.new("BoolValue")
		newValue.Name = house.Name
		newValue.Value = false
		newValue.Parent = Houses
	end
	
	waitForRequestBudget(Enum.DataStoreRequestType.GetAsync)
	local success, houseData
	local retries = 0
	repeat
		waitForRequestBudget(Enum.DataStoreRequestType.GetAsync)
		success, houseData = pcall(HouseData.GetAsync, HouseData, player.UserId)
		retries += 1
	until (success and houseData) or retries >= 5
	
	if success then
		for houseName, houseValue in pairs(houseData) do
			Houses[houseName].Value = houseValue
		end
	else -- if it errors (mostly when player has no data)
		print("Player " .. Player.Name .. " has no data!")
		warn(houseData) -- warns the error message
	end
end

-- House Saving --
function saveHouseData(player: Player, dontWait: boolean?)
	if workspace:FindFirstChild(player.Name.."'sHouse") then
		workspace:FindFirstChild(player.Name.."'sHouse"):Destroy()
	end
	
	local PlayerPlot = player.Plot
	workspace:FindFirstChild(PlayerPlot.Value).CurrentOwner.Value = ""
	player.Plot.Value = ""
	
	local Houses = {}
	
	for i, value in pairs(player.Houses:GetChildren()) do
		Houses[value.Name] = value.Value
	end
	
	local success
	repeat
		if not dontWait then
			waitForRequestBudget(Enum.DataStoreRequestType.UpdateAsync)
		end
		success = pcall(HouseData.UpdateAsync, HouseData, player.UserId, function()
			return Houses
		end)
	until success
end

for _, player in ipairs(Players:GetPlayers()) do
	coroutine.wrap(loadHouseData)(player)
end

Players.PlayerAdded:Connect(loadHouseData)
Players.PlayerRemoving:Connect(saveHouseData)

game:BindToClose(function()
	if RunService:IsStudio() then
		task.wait(2)
	else
		local finished = Instance.new("BindableEvent")
		local allPlayers = Players:GetPlayers()
		local leftPlayers = #allPlayers
		
		for _, player in ipairs(allPlayers) do
			coroutine.wrap(function()
				saveHouseData(player, true)
				leftPlayers -= 1
				if leftPlayers == 0 then
					finished:Fire()
				end
			end)()
		end
		
		finished.Event:Wait()
	end
end)

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