I don’t intend to sound mean, but to be frank, you’re far off ever starting such a website. Given your knowledge, I’d also recommend staying away from such a project until you have more experience in the relevant fields. The reason for this is that there’s a number of intricacies you need to be careful of when building a piracy streaming platform (both technicalities, logistics, and what sort of negative attention you could bring), which you probably won’t pick up if this is your first project.
Having said that, I’d start at looking at back-end dev - this will give you a greater amount of knowledge. After that, you can decide how to approach the problem, e.g. if you’re scraping another website, you’ll need some way of pulling data on the back end (either on the fly, or via some periodic task).
Another aspect to consider would be the logistics, e.g. if you want to host the video files yourself, what sort of bandwidth would be necessary for a certain degree of traffic.
Then assuming you can solve all the technical problems, next to consider is maintenance, promotion and funding.
Language is mostly a concern that newbies have. Experienced developers will often say it doesn’t matter much, so just use whatever suits you.
There’s all sorts of tools/libraries out there that can assist with scraping, or you may decide to roll everything on your own. Every developer will have their own preferences, so find what works for you.
A big part of this would depend on what you’re aiming to get out of the experience. If it’s just for personal education, you might want to take an approach that’s more conducive to learning what you want to know. On the other hand, if you’re more interested in completing a project, you might focus less on learning and more on getting the project done.
If you’re aiming for a private site, it removes a lot of concerns you need to have with a “real” (public) site, simplifying things greatly.