Reading between the lines, it sounds as though there may be other things going on with your computer. I’d suggest - as you have wisely begun, I think - getting Apple to talk you through some basic steps and maybe asking your local Genius Bar to take a look at the disposition of files on your computer… could it be that one or two other concepts are not quite clear to you: for example, don’t move the Downloads folder. Just the RW application?
In general the file which is created by an Apple application - such as a RW project file - will launch its ‘parent’ software.
Yes, that’s a good way to start RW whenever you want to work on a single project; many RW users launch RW itself from the Applications folder when, say, they want to start a new project. That’s a reliable way for you too to proceed.
BTW if you do also have RW 5, you’ll need to follow the conversion workflows to get RW’s add-ons and Stacks etc in the right place.
You may want to consider a refresher on some of the basics before building a RW site that you need to rely on. It will all become clear. Good luck!