I believe using the same keyword as anchor text when it comes to link building will make that certain keyword rank higher than your other keywords
Yes it will make you rank better for this anchor. But keep in mind with a new site, it´s better to vary the linktext in the beginning of your linkbuilding campaign as it looks more natural and is safer if you dont want the sandbox effect. Having fast and many inbound links with the same anchor text may get your new site into the sandbox... So vary your anchors in the beginning. But save the strong backlinks for your main keyword-anchor
Building links with the same anchor text would signal to Google that your links are not natural (or possibly that you are buying links), unless that anchor text is your domain name. I would advise to mix it a little bit.
I don't think so, we should gain links with different - 2 anchor as link if I have financial related site then I can use that kind of anchor Unsecured Loans, Unsecured Loans in UK, Bad Credit Unsecured Loans. so it looks naturals
The more variety the better in my opinion. I often throw in a few links using anchor text I'm not targeting as well to make it look more natural
Do not use same keywords in anchor text. Keep using variations and you will also start ranking for various keywords.