It's generally agreed that a best practice in this regard is to use target="_blank" any time you are linking out to a different website. You should keep your internal links within the same window or tab unless you are linking to a part of your site that's totally unrelated or if you really don't want the user to leave the page they're on.

Additionally, if you are not using target="_blank" make sure all of your pages have clear, easily-understandable navigation, especially when it comes to linking back to your main page.

I used a very similar service that promised 25 edu backlinks for 25 dollars. It was a huge mistake, as all they did was place spam comments on dofollow edu blogs. We actually saw our ranking drop a couple of spaces because of this. I learned my lesson and will never do anything like this again. Hence, I do not recommend this. Any company that charges to get you links usually only acquires poor quality links.

If you're looking for a second opinion, I 100% agree with Thomas.

Having duplicate meta keywords will trigger red flags in the Moz tools and other site quality tools, but only because it's a potential user quality issue. Google doesn't officially use meta descriptions as a ranking factor, so as long as the meta descriptions are appropriate and as best as they can be for what's on the specific page, it doesn't matter how different they are from each other page-to-page. Just keep in mind that this is what shows up in the SERPS, so make them interesting enough to make a user want to click your page over the ones surrounding it.

Here's the real question: if you acquire inbound links to blog.domain.com do those links add to the DA of domain.com or only blog.domain.com? Answer that and you've answered the question.

It sounded like you were describing us word for word. A couple weeks ago, I started a topic about this. http://www.seomoz.org/q/interesting-serp-trend-i-m-observing

I don't have advice either. Just know you're not alone and other people are feeling your frustration.

My belief is that they are not the same at all. With /blog, Domain Authority and Page Rank are being passed on. With blog. you're starting from scratch.