Structure for sorting game assets (?)

Using folders is good. Some other possibilities compared to putting everything in the workspace:

• Use ModuleScripts to store any player data (strings, tables, custom classes, etc). All player data can be stored in ModuleScripts (example below). Technically you can store things like an unparented IntValue if you like.
• Use ReplicatedStorage for all ModuleScripts and assets that will be needed by the client (and potentially the server). (You can move assets back into the workspace to work on them and then put them back where they belong when you're done.)
• Use ServerStorage for assets only needed by the server
• Use ServerScriptService for Scripts and ModuleScripts needed only by the server.

In each of those services I put more folders to group related things (like "Scripts").

Example of ModuleScripts storing how much money someone has:

local module = {}
local playerMoney = {}
function InitializePlayerMoney(player) -- Initialize/load money
	playerMoney[player] = 0
end
game.Players.PlayerAdded:Connect(InitializePlayerMoney)
for _, player in ipairs(game.Players:GetPlayers()) do
	InitializePlayerMoney(player)
end
function module.GetPlayerMoney(player)
	return playerMoney[player]
end
function module.SetPlayerMoney(player, money)
	playerMoney[player] = money
end
game.Players.PlayerRemoving:Connect(function(player) -- Release memory; could also save money to datastore
	playerMoney[player] = nil
end
return module

Do note that since this module

Instead of saving a single number (money), you can modify this to save a dictionary of values, like playerData[player] = {Stats = {}, Money = 0, XP = 100}. Then all your server scripts can access this information simply be requiring the ModuleScript -- the ModuleScript only initializes once and all the server scripts will share the data. (Clients will still need RemoteEvents/Functions to ask the server for this information, of course.)