I have read a lot of good comments here. You might be hard to find the solution that you want from this answers as there is no solution in what is the best technology now.
A lot will argue, but it wont matter.
You dont require the greatest and mightiest in making a CMS. What you need to learn how to actual code.
Since we do assume that you do not have the greatest experience in programming, i believe that you greatest strength currently is in numbers.
That is why i believe that PHP is the language to go.
It might have some quirks and stuff. People might hate it. But it gets the work done for what you require.
It has been out for ever. There is a lot of support. You can easily find question for everything. There are some great frameworks out there, but i believe you should keep away from them.
If you pick up PHP, then it is pretty easy to move to Java later on. But that is another chapter.
So core PHP as it is extremely easy to set up in a LAMP stack. i do home you are using that.
If you dont want to learn CSS and stuff, use bootstrap to get it out of the way. But i recommend trying to write a css on your own so you can learn the basic stuff.
When you are more comfortable with CSS throw that out and use bootstrap.
Then build you PHP CMS from scratch. Split Everything out, seperate classes for queries, functions, html. Look into caching, performance etc.
But most important of all. Have fun doing it.
Hit me up if you want some help/guides/start anything.
In my profile.