1. There are mixed thoughts about the absolute need for a platform by an unknown writer. Many agents only look at the platform (in most cases a blog) when they are genuinely interested in the story that was submitted to them. So, first things first. Perfect the writing and story before spending oodles of time building a blog, because the writing will speak for itself regardless if you have a blog or not.
2. It's really hard to gain followers on your blog if you are only talking about yourself and your unpublished work. So until you are a published author (or even an agented writer) hold off on filling your blog with JUST your own work. Do some book reviews in the genre you read. This will allow you to get to know others, and gain blog followers with common goals and tastes as yourself, thus creating that "built-in" audience publishers like to see when thinking about buying your book.
3. It won't hurt to tie in a well written blog at the bottom of your queries to agents, as long as your blog focuses on writing. I once heard an agent say (yes this was from a conference) she checks out all blogs on the queries she's even remotely interested in. She also went on state that if the writing is dark, or high fantasy, she gets turned off if the blog has a ton of kitties or babies on it. So the lesson there is to match your blog with your writing style. I'm not saying turn your blog into a goth dream or anything, but maybe just limit the cutesy pictures if it doesn't match your writing style.
4. Should you pay someone to overhaul your blog and buy a domain name? No. At least, I don't think it's necessary. But if you want to do it just for the fun of it, then I say go for it, because having a blog that you can be proud of is pretty fun. I just made the leap myself to a professional blog makeover (second one on the link). I was hovering around 430 followers so I thought why not. I'm on there a ton doing posts and just wanted something pretty to look at. Lame, I know. But my old blog design didn't stop publishers from sending me advanced reader copies (ARCs), so don't feel like it's a necessary step.
5. Be yourself. I know this is something you've heard since you were a baby still in diapers, but it's true. People will like you. Let your personality come through, whether it be in your novel, blog post, or a simple comment.