Dude see the tag of the novel you can get the answer for your question

And it's not too risky to kill a bunch of normal humans with ML's current strength

He is alone in the abandoned street it doesn't matter if he shouts or keeps quiet the zombies mostly won't come

It's a system exclusive space in an entirely different dimension which can store things infinitely without detoriating any items freshness or their condition

He has a problem with his soul you will find it later

A kid has turned into a zombie it's pretty normal for his emotions to fluctuate you don't expect him to say "It's a zombie kid never mind his future for me only killing it is necessary as I've already seen a lot of your kind" that doesn't sound cold blooded but rather like a psychopath. MC is mature but he has emotions too. This Novel isn't something where MC ignores everything in the world having his head high telling himself he is invincible and the rest of the world should crawl beneath him as he has already experienced the future he was just a middle level expert in his past life and did not lose his mind and emotions as you normally expect in other novels.

Different zombies have their own growth diffefences.Zombies are fearless of death but that doesn't mean all of them are brainless.

It's every character's aim in the apocalypse to know the truth of the apocalypse and the MC lived 16 years and he didn't know most of the stuff. So you couldn't understand that his desire to know the truth will obviously be more then the others.He also wants to know what was the reason for all the human sufferings and coming to the Killing the child zombie it only slaps him and tells him the harsh truth of the apocalypse that even the children aren't spared.

He was only being harsh with his words because he didn't want them thinking he is some kind of savior and ending up clinging to him.It's not that he doesn't want to help them it's just he himself has problems.

just wait and see how it turns out

Not that many man, you've got quite the imagination the novel focuses more on the story than the romance elements

You will know as the novel advances forward

Sort of....but all the characters have their own importance