How can you change "stage" and "close date" in Opportunities to NOT being required fields?

Not possible. These fields are required by Salesforce at a very low level. What's prompting you to want to make them optional? It may be that if your business process doesn't require using CloseDate and StageName, then Opportunity isn't the best object to use. But if this is for recording revenue transactions, I would strongly recommend adapting your business process to use CloseDate and Stage in some way.

There are some hacky ways to give them default values so that users don't have to directly interact with them, but not recommended. You could use custom code to set a default value as well.

If you're not using the Stage field in a meaningful way for a particular record type, you can remove all but one Stage from its Sales Process. This will force that Stage to be selected when creating new records, and so you won't need to touch it. But if you're using a multi-Stage process but just don't want users to have to pick a Stage at the beginning, you can't do that.