a few questions regarding keywords to choose

Perhaps a great place to start would be telling us exactly the theme, your goals and whatnot.

Under no circumstances is spinning content a legitimate way to generate love from Google. There's only so many ways you can cook an egg - eventually, you'll need ingredients to flavor your food, metaphorically speaking.

You should probably take a step back from your website, and have a good think about what you are doing. You sound like someone talking in 2010. Google has evolved and what you are trying to do will probably not work (at least not the way you are trying to do it).

Your focus should be on actually helping people, not whether or not your article is going to help YOU in Google.

Imagine a real person (or better yet someone in your family that you care about) finding your website, and it's just posts based on long tail keywords and rewritten/spun crap.

Would they be disappointed?
Would they be better off having found your website?
Would they be in a buying mood?
Would they even trust whatever you're saying?
Would your site put them in a mood to trust and click a link that you're suggesting?

You have to break free of this SEO-centric thinking, and start treating people like people. Your readers are the only way you're going to make money, so treat them like it.

You're just building a house on sand, especially because you're not even planning to create your own content.

What's the main topic(s) of your website?...that's the keyword(s) to optimize your homepage for.

Based on what you're saying, you should probably rethink this whole project. Your website should have some kind of vision. If you're struggling with something as simple as what to post first and all you're focused on is keywords, you're going to have a hard time making this really successful.

It used to be very common. However, it was never really useful for anyone. It wasn't useful for the reader in the short term, and it wasn't useful for the website owner in the long term, like I said Google has evolved. Things have changed.

My best advice would be to find something you actually like doing...a hobby or something fun that you're interested in and focus on building a social following, capture those leads and funnel those people to a quality website/affiliate links.

You might do better asking here: Search Engine Optimization

You better to read the theme carefully before choosing the keywords. Your keywords should match your website theme and must be targeted to the actual user as they are searching.