As my pages are dynamic, so if I want to remove noindex after few days as page will have something. Is that google going to consider quickly enough that I removed noindex for those pages?

We have followers, following, friends, etc pages for each user who creates account on our website. so when new user sign up, he may have 0 followers, 0 following and 0 friends, but over period of time he can get those lists go up. we have different pages for followers, following and friends which are allowed for google to index.

When user don't have any followers/following/friends, those pages looks empty and we get issue of duplicate content and description too short. so is it better that we add  noindex for those pages temporarily and remove noindex tag when there are at least 2 or more people on those pages.

What are side effects of adding noindex when there is no data on those page or benefits of it?

We have set up 301 redirects for some subdomains which we are planning to use, but then we changed our focus to main domain. Google has already crawled some of the subdomain pages. As it was duplicate content over subdomains and main domain, we have set up 301 redirects for all subdomains to redirect to the main domain.

We have set up 301 redirects a month ago, but some of the search results still show old URLs. Do you need something extra for google search results to refresh with main domain and remove subdomain URLs from google searches?

We need rankings to be passed new URLs.