Easy Profile - Joomla Extension

1. Yes, you can set all fields on required, and in option of Easy Profile to Yes at parameter "force the compilation of the required fields on login", when user log-in the system redirect on Edit page, only when the user have fill all required field can view the site. Alternative, you can set redirect for first login (or all logins) to edit profile page.
You can try these on Free Version

2. you can set in Easy profile configuration access level to see other profile. You can try these on Free Version

3. I do not know if I understand correctly, if you mean like our site, Yes. You can try these on Free Version

4. No, but you can use our trigger plugin (see docs at https://www.easy-profile.com/docs/44-triggers.html) You can try these on Free Version
example
if($data['alias_of_field_to_check']==5) $data['alias_gender_field']='female';

one thing
I do not think you can create 100 fields, Easy Profile not have a limit but MySql have an hard limit of columns(read here https://www.easy-profile.com/support/can-i-make-any-number-of-tabs,-fields.html#reply-495) (1 field=1 column in DB). I think you can create a maximum of 70/80 fields.