Your regex excludes spaces, and includes all punctuation as well as numeric characters. To remove commas, dots, and spaces is easy:
But ... you will have to work out rules for you second requirement fairly carefully - when does a space get removed? Is it "not after a word of sufficient length"? Or "not between two words of sufficient length"? What about "I am a human"? Should that remain as it is, or have some or all spaces removed? What about "I, a human ..."?
I suspect that you are going to stress Regexes too far to get maintainable code and meaningful results, and that you will need to define your problem to yourself a load better before you even try to sort this - with or without a Regex!