Creating chunks with Perlin Noise? (Help!)

Hey there!

I've been bored out of my mind with this whole "Not having a job due to quarantine thing" & have been messing around with Perlin noise in generating terrain. I've got it working pretty nicely, looking spectacular if I may say!

Now, to expand upon the question, which is not yet asked: How do I load in chunks seamlessly without causing colossal lagspikes? So far my code is using for loops per dimension size to load in the first starting chunk (I found the initial code in a YouTube video, and thus I have expanded upon it for a cleaner terrain generation). I generate the seed using math.random(0, 10000000) for... randomness. Now, I can't just simply load in a whole new chunk because this method is using thousands of blocks per chunk, which would cause immense lag. So I was thinking of despawning around 10 blocks behind the user and 10 in front per increment. But I still have no way of knowing how to do this.

If you have any question please let me know! Code is below.

game.ReplicatedStorage.RemoteEvent.OnServerEvent:Connect(function()
    local n = tick()
    for _,v in pairs(workspace.TerrainG:GetChildren()) do v:Destroy()end
        local mapxsize = 100
        local mapysize = 40
        local mapzsize = 100

        local seed = math.random(0,10000000)
        local noisescale = 50
        local amplitude = 20
        local blocksize = 3

        local lastBlock

        for x=0,mapxsize do
            for z = 0,mapzsize do
                for y=0,mapysize do
                    if y == mapysize then
                        local lastPart = Instance.new("Part")
                        lastPart.Material = Enum.Material.SmoothPlastic
                        lastPart.Anchored = true
                        lastPart.Size = lastBlock.Size
                        lastPart.CFrame = CFrame.new(lastBlock.Position.X, lastBlock.Position.Y + blocksize, lastBlock.Position.Z)
                        lastPart.BrickColor = BrickColor.new("Bright green")
                        lastPart.Parent = workspace.TerrainG
                        local treeblock = math.random(1, 1000)
                        if treeblock == 12 then
                            local tree = game:GetService("ReplicatedFirst").Tree:Clone()
                            tree:SetPrimaryPartCFrame(CFrame.new(lastPart.Position))
                            tree.Parent = workspace.TerrainG
                        end
                        local rockblock = math.random(1, 1000)
                        if rockblock == 12 then
                            local rock = game:GetService("ReplicatedFirst").Rock:Clone()
                            rock:SetPrimaryPartCFrame(CFrame.new(lastPart.Position.X, lastPart.Position.Y + 1, lastPart.Position.Z))
                            rock.Parent = workspace.TerrainG
                        end
                        local grassblock = math.random(1, 50)
                        if grassblock == 12 then
                            local grass = game:GetService("ReplicatedFirst").Grass:Clone()
                            grass:SetPrimaryPartCFrame(CFrame.new(lastPart.Position.X, lastPart.Position.Y + 2, lastPart.Position.Z))
                            grass.Parent = workspace.TerrainG
                        end
                    else
                        local xnoise = math.noise(y/noisescale,z/noisescale,seed) * amplitude
                        local ynoise = math.noise(x/noisescale,z/noisescale,seed) * amplitude
                        local znoise = math.noise(x/noisescale,y/noisescale,seed) * amplitude

                        local density = xnoise + ynoise + znoise + y
                        if density < 20 and density > 10 then
                            if density <= 19 and density > 10 then
                                local rand = math.random(1, density)
                                if rand == 3 then
                                    local part = Instance.new("Part")
                                    part.Material = Enum.Material.SmoothPlastic
                                    part.Anchored = true
                                    part.Size = Vector3.new(blocksize,blocksize,blocksize)
                                    part.CFrame = CFrame.new(x*blocksize,y*blocksize,z*blocksize)
                                    part.BrickColor = BrickColor.new("Dark stone grey")
                                    part.Parent = workspace.TerrainG
                                    lastBlock = part
                                end
                            end
                            local part = Instance.new("Part")
                            part.Material = Enum.Material.SmoothPlastic
                            part.Anchored = true
                            part.Size = Vector3.new(blocksize,blocksize,blocksize)
                            part.CFrame = CFrame.new(x*blocksize,y*blocksize,z*blocksize)
                            part.BrickColor = BrickColor.new("Brown")
                            part.Parent = workspace.TerrainG
                            lastBlock = part
                        elseif density < 10 then
                            local part = Instance.new("Part")
                            part.Material = Enum.Material.SmoothPlastic
                            part.Anchored = true
                            part.Size = Vector3.new(blocksize,blocksize,blocksize)
                            part.CFrame = CFrame.new(x*blocksize,y*blocksize,z*blocksize)
                            part.BrickColor = BrickColor.new("Dark stone grey")
                            part.Parent = workspace.TerrainG

                            lastBlock = part
                        end
                    end
                end

             end 
        end
        local m = tick()-n
        print(m)

end)