Wheres the best place to put all your sound effects/in-game music?

Is it in StarterGui? Is it Soundscape?

I would say you should make a Folder then name the Folder SoundStorage, make a StringValue for each sound. Rename each StringValue then if you named one SmashSound then put the Smashing Sound ID into the value. Do it for all, then after you done all fo that. Insert a sound into the Workspace and name it SoundPlayer, make the Sound ID to nothing. Now put the folder into ReplicatedStorage or Lightning, after all of that make sure loop is on if you want it to loop and set the sound volume to 0

If you are making a button from StarterGui then put this script into the button

-- Example of the Smashing Sound
local button = script.Parent
local sound = game.ReplicatedStorage.SoundStorage:WaitForChild("SmashSound') -- Finding the smash sound
local player = game.Workspace:WaitForChild("SoundPlayer')
button.MouseButton1Down:connect(function()
	player.SoundID = sound.Value -- changes the song
	player.Volume = 0.5 -- sets the volume high
end

With this script just change the local sound variable to define other sounds and then you can play any sound.