1. Although all pages in example.com are being 301 redirected to example2.com, why are my users now about 50% of old user count?
If you're using the same tracking code and all pages have been redirected properly, the lower numbers you're seeing are likely due to a change in search engine results because your domain has changed.
This is to be expected, and will take some time to regain your previous search engine results while the search engines build trust for your new site. Here are some things that should help with this:
2. Do I need to create a new Google Analytics property for the new site?
You don't need to create a new property, however, you should update the domain in your URL's within Google Analytics. Here's how:
Select the property for the old domain from your Account Home page.
Admin from the top-right corner of the page and select
Default URL from:
http://example2.com, and click
...in these 5 days that I have moved the site the number of users are less but the monthly number of visitors and unique visitors are increasing.
That is to be expected too - since the domain is new, visitors who visited your previous site are now unique to your new site.