Are ukuleles good/easy starter intruments?

I'm a 13-year-old girl, I turn 14 in October and I'm getting a ukulele for my birthday, my plans are to "finish" the ukulele -- or in other words, see if I like it, then focus on "mastering" it, then I will get a guitar as a level 2 kinda thing later on. I might throw in a harmonica to harmonize w/ the guitar, too. I was just wondering if this is a good action plan? I've wanted to be a musician for a while, and I'm not getting any younger, so I figure now is the time, am I right? From what I've heard I have an okay voice, so I was thinking adding a uke or a guitar could really spice that up. Okay, I'm waay off topic now, what I'm really wanting to know is a ukulele easy to learn/master and is a guitar really an accurate level 2? Thanks. :)