To improve security, we will soon start forcing password resets for any account that uses a weak password on the next login. If you have a weak password or a defunct email, please update it now to prevent future disruption.
Yes. Unless it comes with license requirements that says otherwise. Some people release free stuff and require you to credit them if you use their stuff, things like that.
Importing to Unity/Unreal and using the assets interactively - no. You need to purchase an interactive license for it if it is not included. EACH asset must have an interactive license, not one for all.