Molds of PhD thesis from more than one idea
This varies a lot from field to field, so take this with a grain of salt. Before I started my PhD, I envisioned doing lots and lots of stuff. Unfortunately (or fortunately actually), that isn't how academia works. Developing a (good) project takes time. Also, more often than not, easy and good ideas have already been explored which means that, if you want to work on a particular topic, you have to build on top of what other people have already done. For instance, during my PhD, I developed 4 different projects over a period of 4 years. And that is considered above average in my field. Talk to your supervisor once you have one (or if you already have one). They are there to guide and will provide with the answers that you need.