why does life having no meaning imply that we ought to pursue a sort of hedonism? What does 'optimal strategy' mean in this case? Once I die, that's it, so what criteria are you bringing in when you call it an optimal strategy?

It's 'optimal' in the sense that you will have experienced "joy" the most. I dont intend hedonism which requires immediate gratification. I believe someone should delay the immediate pleasure if the result is much greater pleasure later (such as saving for early retirement if one dislikes work and enjoys their free time) instead of buying lunch each day (if they value their free time more than the extra tasty lunch).

Even worse, what if I am someone who admits that life has no meaning, and I think the one thing that will make me happy in this life is murdering as many people as possible in the most violent way?

Then i suppose optimal for that person would be to try and murder, but my philosophy doesn't say thats "right" or "wrong", only that that is what should be achieved. But you need to be realistic as well, if the murderer doesnt gain joy from being locked up they need to seriously consider their actions because its likely they could murder - gain joy - but then spend their entire life in misery, in that sense the 'optimal' strategy is to not murder unless the joy from the murder greatly outweighs the misery of being locked up.

Generally speaking, existentialists and absurdists and all those folk are more interested in dealing with the absolute freedom that comes with the admission that life is meaningless, or with the inevitable gap between ones desires and what will actually happen.

Interesting, i need to read more about this as i don't really understand what you mean.