There is a huge variety in the complexity of sites on the internet. A web site must convey the proper information in a manner that looks professional and is easy to navigate.
Most web hosts will offer WordPress services for free. There is a learning curve to using WordPress, but it is the most commonly used Content Management System in use today. I do not use WordPress, as it was originally built for Bloggers and is still optimized for blog sites.
HTML is the language of the internet. It is not dificult to learn, but there are many extensions that are required to make truly effective web pages.
Cascading Style Sheets (CSS) and JavaScript are used in most web sites to improve their utility.
Chances are that the majority of users that access your web site will be using a smart phone or other mobile device. It only makes sense to build a website that is optimized for mobile devices.
Bootstrap is a great tool to allow for mobile-first design.
A consistent theme that includes colors, fonts and formatting will enhance the user's experience.
You don't need to recreate the wheel, as many themes are available. The US government has a well established set of themes they require for web ssite design.