[Ethical] Need help with Pentesting

I am currently in school and have been assigned a fairly big project with the topic being Pentesting, I am fairly confident in my skills but I am completely stuck.

I was hoping if someone more experienced then I could help out and point me in the right direction I would greatly appreciate it.

The Scenario:
I am using a VPN to connect to the internal network and my objective is to gather as much information as I can about a specific IP, this IP also has a LAN behind it with a tuff firewall.

The firewall itself blocks ICMP packets and others making OS Detection difficult as the ports show that they are either open or filtered, the open ports that I am aware of currently are: TCP: 80 (IIS Webserver 10.0), 135, 445, 5357, 5985, & 49668 UDP: 137

I am fairly certain it is Windows 10 1809, or a Windows Server 2016/2019.

NOTE: Social Engineering will not work nor will any sort of relays as there will be no user on the target so essentially no user created traffic as this is a test environment.

Thanks.