Hey, I will be getting into the PC gaming and I want to know if I will be able to get 144 fps with these components. I have a i5 8400 and a GTX 1070. I mainly play Rainbow Six Siege and I don't know if these choices were a mistake.
Try posting your complete build so we know your Motherboard, RAM.
From my personal experience, I have played R6S on a non-gaming laptop with a gtx 950m and reached 60fps easily.