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So true. Buy up all that you can afford as quickly as possible.

I'd be more inclined to put the time and resources into optimizing your main site. Build some links, make sure your on page is flawless.

I had heard something about that as well, but I still think .com/blog reads better/looks cleaner than the blog.abccompany.com

Of course that is pure personal preference

Unless policy changes 301 should continue to work indefinitely. I've never seen (noticed) this depreciating or expiring over time.