The answer to #4 honestly is not as simply as a percentage … you really need to look at the competition set to assist with this direction.
I personally like to see a much higher percentage with CTA “Call to Action” anchor text links as this is more natural; but this depends on the research. Also, try to plan for the future … exact match is over used considerably within gaming, but it still has value. You can also mix keywords with CTA and Brand as anchors …
“keyword” @ Brand
“keyword” via Brand
Discover “keyword” from Brand
CTA for “keyword” @ Brand
Using the examples above you can still mix your keywords into longer anchors and still pass the anchor equity to the page you are linking to. Be creative …
URLs are also able to pass anchor equity:
Find the best domain names to register
This passed anchor equity (in its simplest form) with “bingo brand” “keyword keyword” – this is another benefit of using SEO/User friendly URL structures.