The blog doesn't need any fancy features, but should fit in with the look of the website. Should I customize Wordpress or is there an easier way I'm missing?
I'm one of the founders of Perch CMS (http://grabaperch.com) which has a blog add-on. One of our core features is that you can drop Perch and any of the apps into an existing website - without needing to put the entire site into a theme etc. So it's a different approach to something like WordPress.
The video tutorial takes you through a full install of Perch for content management but the videos towards the end cover dropping in the blog app and customizing templates http://docs.grabaperch.com/video/tutorials/swift/
There are rather good SEO reasons not to do that - specifically, if the blog becomes popular, the search engine ranking won't translate to the main site if the blog's on a separate subdomain.
www.foo.com/blog/ is almost always a better idea than blog.foo.com unless you don't care about organic traffic.
I think, short term easiest and most flexible would be to just write HTML. Long term it would be best to just make it right. I'm little surprised that there is not any copy paste solutions (with ads maybe). I guess most are going with Wordpress. I may have to change that..
Easiest way would be Tumblr I think. Write there, use the API to retrieve your posts and display it the way you like. Might be more tricky to use everything (comments, posts and stuff) from your website though, never tried it.
How is it easier to use than Tumblr, where there is virtually no setup involved (besides pointing a domain to your blog perhaps, and it's completely free).
The video tutorial takes you through a full install of Perch for content management but the videos towards the end cover dropping in the blog app and customizing templates http://docs.grabaperch.com/video/tutorials/swift/