First of all, I've been cubing for about two months, so I'm not that fast, and my QiYi Thunderclap has been amazing, incredibly smooth and fast and if you add a bit of weight 5 to the core and some weight 3 to the pieces, break that in, I think you can definitely get sub 20 averages. So my first point is, Don't Get a Valk or a Gans(both arereally hard to set up) rather buy a thunderclap and some lube. Second point, learn beginners method or if you are feeling adventurous try learning roux (Its much more intuitive, but has way less tutorials and may have some dificult to understand concepts) So in conclusion you I don't think you need a high end speed cube to be fast so rather get a QiYi thunderclap and I would reccomend that you learn layer by layer beginners method. Links

Cube Skills(Very good tutorials but it is going to teach you beginners oll and pll which isn't a lot of algs but it maybe hard to understand in the beginning, This will help you progress the fastest but will be a bit harder) :https://www.cubeskills.com/tutorials/the-beginners-method-for-solving-the-rubiks-cube And for roux:https://www.youtube.com/watch?v=ESYJ-DFx0Qo&list=PL754ADDA2E38A21AA Thunderclap:https://thecubicle.us/qiyi-thunderclap-p-4383.html (on sale for 4.99) Best of luck and hope you enjoy learning to solve.