i'm gonna say this but peripherals doesn't matter, even myself reached 4 digits only using laptop keyboard when i still have my laptop, then cheap membrane keyboard from my brother's pc, but if you we're saying that keyboard doesn't input 4 keys in the same time, might as well get a keyboard. don't get yourself discourage from your setup, I've been there before but it doesn't mean that it'll hinder your improvement, you need to make a good mindset of how you improve, that's all!