First question: I'm writing a cover letter, and I can't decide between cutting it in half or not as it feels smoother as one sentence. Maybe you can help. I am particularly interested in [firm name] because your experienced staff and large client list would offer a great learning environment, and I would enjoy living in temperate California, where I could bike year-round.
It is not a run-on. A run-on is grammatically incorrect it consists of two improperly joined sentences. The preceding sentence is a run-on. But your sentence does ramble. I would divide it into two or three sentences. One sentence should express one idea.
not only does it ramble ineffectively, as cog points out, but if aimed at a literary agency, it doesn't make much sense as a reason to choose an agent...
I agree with Cog that it's grammatically sound, and I also agree with him that it rambles. Does a client list provide an environment? Is there a second, intemperate, California? It's looks as if you haven't fully thought about what it is you want to say.
