you are getting error from the mysql server. That means there is no firewall or port configuration issue. you need to grant proper privilege to the user connecting to database.
Connect to mysql as root and run grant command.
grant all on <DB name>.* to <user name>@'<hostname>' identified by '<password>';

<host name> is the exact name or IP address of front end, which you are seeing in error message. You can also provide % to allow permission from any host.

What's about Objective-c and Node.js?

Count me in, bro ! I just bought a rMBP for ios app development. It would be nice to share your experience with newbies like me. BTW, the price of Macbook Air is as closely as PCs, so it doesn't cost that much money indeed. In Xcode, there are default emulators for testing.

No matter how hard it is, just be calm at exam. Make notes on important things and do enough practice to help your remember things you just learned.