Sounds like you're off to a good start! I'm in the same boat. Trying to put it together on the fly, with no teacher. (: We'll all muddle through together!
I'd say, my teacherly advice (I have taught, just not music): keep going with the exercises, but also try writing something longer. A whole piece. Say, about three minutes of music. It will not be perfect, but it will get you motivated in the way that short exercises just won't. And it will give people here more to give feedback on, and you more of a chance to figure out what you still need to know. It's hard to give much feed back on something as bare bones as what you've posted. There just isn't much there to comment on. I want to see what you do with the theme for the next page of music... Then we'll all know that you need to vary your rhythms more, or your chord progressions are all the same, and all don't quite work because every time you...
And the sooner you write something substantial the better. Otherwise you'll be scared of it, and you'll just keep putting it off.
It's not going to be good. Let's get that out of the way right now. It's not going to be good. There. Now, knowing that, what is there to worry about? Get out there and get writing! You are going to have to write a whole lot of awful stuff before you start writing things you like. So the sooner you get the writing of the awful stuff out of the way, the better.
In the game "go," they say, "lose your first 100 games quickly." No sense trying to over-think every move. You don't know enough yet to be thinking about the right things. You ARE going to lose the first 100 games. It's just a question of whether it takes you 2 years to play them, or 2 months. Don't let it all be so precious to you that you are afraid to make a move. Just get writing, knowing that the sooner you throw out the first 100 pieces, the sooner you will write the next 100, and the next 100. (:
And keep studying. Me too!
Here's one of mine so we can share the agony of our current awfulness: http://youtu.be/Cn4YwJ8Fmws
That's maybe the third thing I've written, but I'm pretty proud of it. The notation is terrible, I'm sure, and I have no idea what the chords are. But I'm still proud of myself.
Here's one that's maybe the fourth thing I've written. http://youtu.be/PCLxpE_rkI0
Also bad, but it's my baby, I did it all by myself, and I even wrote the text. So I'm proud of me, and pumped to keep going. You too. Keep going. And ask questions when you have them. (I won't know the answers either, so I'll eavesdrop on other people's advice.) (: