I did found the same issue for my site last months. the issue was my referral traffic and some organic (spam keywords) traffic was drastically increased by spam traffic that make 90% to 100% bounce rate. Check out your referral traffic and organic, this can be the issue too.

No, it won't create any confusion for SEs if you are using the schema in proper manner like mentioned here, as per my opinion Structured data is a great idea to display your business in SEs, and it is definitely appreciated by SEs. This is also a good article about Schema https://blog.kissmetrics.com/get-started-using-schema/

Hope it helps

Yes, I have done for most of my sites manually but after reading this article I found some interesting points like i need to use Structured data markup helper.

I have never seen or even heard that google penalize any site for Bold, Italic or underline. It is okay to use B.I.U with your content but as per my opinion you need not to B.I.U every keyword. you just need to write content for Users not for Search Engines, just B.I.U the words that should be highlighted on your content.

for Ex. if you are writing content for your product then highlight its Main functionalities. Hope it helps...

Yes, this is called Shared web hosting service. let me give you a link

https://en.wikipedia.org/wiki/Shared_web_hosting_service

Hi,

Creating robots.txt file for the site is one of the most important thing, you need to understand your website or stores basic needs what to keep private and what to make public; I think you need to block some part in your magento site like your search pages (?*sid) and admin pages, user dashboard pages, here is an example links Robots.txt for Magento and Robots.txt File Examples