How do I get a model to disappear and reappear using scripts?

If I were you I wouldn't choose making everything in the model transparent and can collide false. Reparenting would be the best option in my opinion.

Example

local Maps = game.ServerStorage.Maps

local function HideMap(MapName)
    if Workspace:FindFirstChild(MapName) then
        Workspace[MapName].Parent = Maps
    end
end

local function LoadMap(MapName)
    if Workspace:FindFirstChild(MapName) == nil then
        Maps[MapName].Parent = Workspace
    end
end

run a loop to get all the things inside a model for each small increment and get all the parts and lower the transparency, im not making the script for u, but telling u how to do it