Well, Arduino Projects are only useful if you have something that needs to be automated. Otherwise they are just fun toys.
What I would do is, set up an computer, and on it a nat, web-server, and maybe run some website. As for music the possibilities are pretty endless. Maybe you could use some arduinos or raspberries for musical things!
Anyway the must haves are a soldering set, a way to manage your electronics and cabling, enough desk space, and computers.