if you'd take a lot of stars and planets, and put them together (but not too close together), then at one point if you make this large enough, it'll also be a black hole: there appears an event horizon around all this matter. But inside of it are still stars with gaps between them, maybe some planets orbiting around them
Are you suggesting gravity doesn't exist inside an event horizon? O.o
All of the matter making up these stars and planets would gravitate towards each other and become one massive object.
And if they are far enough apart that gravity can't pull them all together, you get.... what? a "solar system"? Clearly there's no event horizon around us, because then we wouldn't be able to observer other solar systems. So lets go bigger... galaxies? No, we can see other galaxies too, so no event horizons around them either.
Basically, if your body of matter isn't dense enough, then you're not going to get an event horizon because light should be able to easily move away from your body of matter. I'm sure some physics major could supply you with the appropriate equations (i'm just a lowly comp sci geek... and should be working and not trying to explain this right now! lol) but simply put: gravity gets weaker as you move further away from the center of your body of mass. If you have light moving about freely inside your event horizon... then, um... you're using the wrong definition of "event horizon".