Open-source software is software that is freely available and can be modified and distributed by anyone. It usually requires very little technical support and has no licensing fees. Therefore, it would be the lowest cost solution for an application that does not need much support. References: https://www.comptia.org/training/resources/exam-objectives/comptia-server-sk0-005-exam-objectives (Objective 2.3)

A headless installation is an installation method that does not require a graphical user interface (GUI) or a monitor, keyboard, and mouse. It can be done remotely through a network connection or a command-line interface. A headless installation is suitable for a server that has limited resources and does not need a GUI.
References:
CompTIA Server+ Certification Exam Objectives1, page 14
Server Management: Server Hardware Installation and Management2, Module 2, Lesson 5

A crash cart is a mobile device that consists of a monitor, a keyboard, a mouse, and a network connection. It can be used to access a physical server that is not responding to remote management software or does not have out-of-band management cards configured. The technician can connect the crash cart to the server using a VGA or HDMI cable and troubleshoot the server locally. Verified References: [Crash cart], [Out-of-band management]

Drive encryption is a form of data-at-rest encryption that encrypts the entire hard drive or solid state drive. This means that all the data on the drive, including the operating system, applications, and files, are protected from unauthorized access. Drive encryption is usually implemented at the hardware or firmware level, and requires a password, PIN, or biometric authentication to unlock the drive. Drive encryption is the most comprehensive and secure way to achieve data-at-rest encryption, as it prevents anyone from accessing the data without the proper credentials, even if they physically remove the drive from the server.
References: CompTIA Server+ Study Guide, Chapter 9: Security, page 367.

Port 443 is the default port for HTTPS, which is the protocol used for secure web communication. HTTPS uses SSL/TLS certificates to encrypt the data between the web server and the browser. Port 443 is commonly used for web servers that need to provide secure services, such as online banking, e-commerce, or email. By allowing port 443, the administrator can access the web server's interface and manage its settings1.
Port 3389 is the default port for RDP, which is the protocol used for remote desktop connection. RDP allows a user to remotely access and control another computer over a network. Port 3389 is commonly used for remote administration, technical support, or remote work. By allowing port 3389, the administrator can connect to the web server's desktop and perform tasks that require graphical user interface2.