You are under no obligation to blog about anything. Personally all my blog entries are on the professional level. I rarely blog about personal activities. Others do. It all depends.
Yes if people know your real legal name they can find you. But as I already said, they can find you through your IP address. The latter is simply easier. Yes it will make life more difficult for a creepy person to find you, but if you are that worried about it, I wouldn't do public appearances either. Who knows if someone from your past might blow a cover? An unsuspecting bookseller filling out a cheque to your real name accidentally shares it with someone. Your publisher has the information, as does your agent. And if the person is really crazy, they could just follow you home after the event, or to your hotel. Unless of course you plan on switching cars or something.
Honestly, I just think you are being too paranoid about all this. Truly. I think it is wise to be safe and careful, and definitely to not make it easy for people. But if the only reason you are creating yourself a pen name is to avoid the crazies, I don't think that's a good reason. Because it's the crazies who will find a way. People create pen names for good reasons. Sometimes it's for an existing author to distinguish between two genres. Let's say they write children's books and erotica, thus having two different names helps to make sure a kid doesn't see your name in another section and go, "Ooh I like her books!" Sometimes it's for an author to attempt to write without the reputation they already had. Stephen King did that. Note that everyone now knows Stephen King did that. Sometimes it's simply because the author's real name is too complicated to spell or pronounce. Sometimes it's to create a character, ie Lemony Snicket. But the only time I know of an author who uses a pen name to avoid crazies is when they avoid the spotlight entirely, when their entire existence is a mystery. No one has ever seen them.
Anyway, as to the actual blog question. Of course, create a blog about writing. In fact I am firm believer in blogs being as professional as possible. This is for two reasons, one I just prefer reading professional blogs, and two because everything you put out there is subject to scrutiny. I think this is where your paranoia will be most helpful. There are careless people out there, and sometimes I can't quite believe the things people willingly put out on the internet. I mean, seriously.
At any rate, it's your decision. When it comes to publication time you can chat with your agent about the pen name thing, express your concerns and see what she recommends. Maybe she will be totally opposite from me, that is quite possible, I'm not always right, lol. But right now, you don't need to worry about that. Focus on your blog, be professional, and I think you should be okay.
