I have accumulated a lot of third-level hard drives, and I am very short of money, can I send Dr. Bao more hard drives and get a lot more money for it than he asks in the letter, or will he not pay?

and another stupid question, what key combination do you need to press to craft an item?

You can send more, but it's not recommended, as if you send more boxes per day -- including the daily boxes -- you'll get a good week review, which can reward you with more money. Like, 500+. However, if you need more ways of making money, you can sell trash, sell food if you have more than enough. There's tons of ways to get early bits of money, and I've covered a lot of it if you wanna visit my tips thread sometime. Lots of tips that might help you!

As for crafting, if you have enough materials on the bench to craft scrap, or a recipe, you'll see a new option pop up on your radial menu.