You should ask yourself a few key questions:

1. If you're starting out do you have the time to do product dev AND a blog? Blogging can be very time intensive.

2. Is the blog part of your marketing or just a place to park notes about product releases?

3. If it's part of your marketing plan is a blog the best investment of your time and money? Does it give something to your audience?

4. Are you writing this blog, or is that the job of someone who is doing your content marketing?

I'd first figure the basics out then worry about hosting...

yup good questions, i guess i'd like to know how the marketing of a blog works, what's the value... where it should sit in the priority on the marketing budget/plan?

There isn't a silver bullet answer for that: It depends upon the specifics of your marketing plan — and marketing is really an art form as as anything else so there are no hard rules. You should think of what the product is, who you're trying to sell to and then come up with the details. But I think with a startup you need to spend your initial energy on the product and then think how you would market it.