Hi,
I viewd the site model you like to build. And on the points you like to cover on the website,
1. We can group videos by category or by theme. It can be done using mysql queiries and php
2. Yes, can do it.
3. To add videos you can use the wordpress template builder and the theme admin wher it is possible for you to add vidoes and the text to it,
4. Yes, you can change the menus later.
Regarding the wordpress, you can install it ina nay domain as long as you have the cpanel login credentials with you. It is as easy as a few clicks to install wordpress to your domain,
The process is, once you finalize the design, we will convert it to wordpress theme, which is a bit different from ordinary html pages, then add contents, sub pages, images and vidieos, Then we can have a one to one teamviewer session to teach you how to add or change the contents, so you can do it as you like to do it,
Looking forward to work on your projects,
Best regards,
TGS