Server controlled Menu GUI - Where to begin?

So I am completely revamping my game, but being away from Roblox for about a year I'm not too sure where to begin with this.

I want to change the message and hints to a GUI and also create a new menu GUI system so that the menu disappears once the race starts. I'm not too sure where to start, this is all fairly new to me. (This would also mean I don't have to go for a lobby - All is done from within the menu!)

Here is the script as it is below - It's very inefficient and converted from an old Zombie Survival game. It uses a lot of 'old school' coding.

Delay = 10
ZombieAttackTime = 45 

function hint(text,time) --Hint Function
    local Message = Instance.new("Hint",workspace)
    Message.Text = text
    game:GetService("Debris"):AddItem(Message, time) --Add Item from Debris service
end

function message(text,time) --Message Function
    local msg = Instance.new("Message",workspace)
    msg.Text = text
    game:GetService("Debris"):AddItem(msg, time)--Same thing
end


while true do

    for i = Delay,0,-1 do --Changed this to this format
        hint("The Next Race will begin in " .. i .. " seconds", 1) --Changed the hints into functions
        wait(1)
        end
    message("Course: Original by Michael007800", 4.5)--Same thing with messages
wait(5)
    message("The race will start soon!", 3)
    game.Lighting.Map1:clone().Parent = game.Workspace
    game.Workspace.Teleport:remove()
    game.Workspace.Lobby:remove()
wait(15)
    game.Lighting.Lobby:clone().Parent = game.Workspace
    game.Workspace.Lights.Sequence.Script.Disabled = false
wait(6)
    script.Parent.Parent.Gates.Release.Disabled = false
    script.Parent.CanCollide = false
    wait(5)

    script.Parent.CanCollide = true
    game.Lighting.Teleport:clone().Parent = game.Workspace
        for i = 1, ZombieAttackTime*1 do
            hint("The race will end in " .. (ZombieAttackTime-i) .. " seconds", 1)
        wait(1)
    end
    message("THE RACE HAS ENDED!!!!!", 3)
    game.Workspace.Map1:Destroy()
    script.Race1:stop()
    script.Parent.CanCollide = true

end

If not revamping the entire script, where would I begin with this?