AMP websites shouldn’t replace the whole website, they should only really be used for content pages.
Crawling Form Action Links
Form actions or links are used as a way to discover new pages but not to pass pagerank so don’t need a rel=nofollow tag.
Google does NOT use Google Analytics Data as ranking factors, such as Bounce Time etc.
The ‘In-depth articles’ feature still exist, there is just a slight UI change in the SERPs.
Cross-Linking with Sister Websites
A small amount of sister websites sharing links is acceptable, but if there are many websites with cross-links then Google will start to consider it spam.
AMP Pages & Structured Data Errors
AMP pages and ‘structured data’ items need to have no errors to be indexed properly.
Google Analytics AMP Support
Google Analytics supports AMP pages and also does not show search terms.
If Googlebot detects that a server is taking a while to respond (probably due to heavy traffic) then it will crawl slower to accommodate.
Image Alt Tags
There is no limit for image alt tags.
Images Affecting Ranking
Having images in a page (whether they’re working or not) doesn’t affect ranking in web search, but higher quality images are ranked higher in image search. Also, images are connected to landing pages so content within the landing page is used as a factor for ranking the image in image search.
Flat vs Hierarchical Structures
Google does not have a preference regarding flat or hierarchical structures.
It’s not compulsory to have a wikipedia page for your brand, Google uses a variety of websites to gather data for the knowledge graph section.