Which specific part are you having difficulty with? Is it the whole game concept or a certain aspect of it?
You'll need to store the amount of money in a LocalStorage so that you can add to it and retrieve it later on. Everytime you retrieve it (or set it), you can put it in your global variable and then set the text to the global variable. Check out the LocalStorage documentation, which is really helpful if this is your first time dealing with LocalStorage.
When changing layout, if you don't want to display the money UI, then don't include it, destroy it, or hide it.
There is no switching of perspective really. You just define it by what behaviors you use and how you construct your levels. For example, if you have a player and put a Platform behavior, then you have a side scrolling game. Add solid objects for the player to jump on. If you want top-down, then give your player 8-directional movement and design the layout as such. You can disable or enable if you need to have both.
There are some basic fundamentals you are curious about so let us know if you have specific questions to the challenges you are facing. Good luck! :)