Modern Web Development Practices

So, I've mostly been working on the front end of websites, and have had some experience in back-end development in the past, but I want to learn a some new modern practices used nowadays to develop websites.

Up to this point if I had to fiddle around with back-end development I would usually resort to WordPress to get the job done, however I like to learn other techniques to firstly have a better understanding of back-end development but also have more control of the sites I develop.

Essentially my questions are,

If I were to develop a forum type site what sort of framework should I be looking for ? and frameworks for e-commerce sites?

Also how do frameworks like ruby on rails and jekyll, scale in terms of users and data ?

A point in the right direction is much appreciated , thank you.