A umask is associated with an individual user, so you can't really set it on a project or a directory. Perhaps you are talking about setting a mode (basically the opposite of a mask)? For instance, you probably want `chmod 700 /home/*` to set the permissions on home directories to be rwx for only the owner. Please add some more description to what you are trying to do or the final outcome that you are trying to achieve.
You don't. umask is a single value that is set on a per user basis. It affects all directories and files that are created after the umask value is set (and none before the value is set).
You can use chmod to set permissions, recurively, using the -R option. For example:
sudo chmod -R 700 /home
As @Forrest said, we'd relly need to know more as setting 700 on /home is probably a bad idea.
As for "projects," which implies some sort of collaboration, you'll want to look into the following: chmod, the setgid bit, chown, and file access control lists (getfacl and setfacl).