Really sorry to hear about your loss.
Ultimately if your friend lived a wonderful happy life with his wife, children and friends, then you should remain happy even though he left quiet abruptly. I would suggest not to turn to alcohol and weed as a coping mechanism for your grief. Now it may be hard to put this into play, but staying strong at a time like this will only help you with the ease of burden which has come about from your friend passing. Sleeping will do you a world of wonder. Like Aklan said, you will definitely regret it, if you lose the chance to say goodbye properly at his funeral.
I've always lived by the mantra that if your heart is in pain emotionally, sleeping will ease that pain. Now it may sound silly, but honestly it works. If you get some rest before the funeral you can properly put together how you feel, and what you want to say to your friend on the day of his Funeral.
Now I don't know if you believe in the afterlife, and you say there are many questions to be asked, but no answers to come. I suggest even if you believe that there wont be any answers, that you still ask the questions. For me I've always believed that those who pass can still hear you. So I believe your friend will hear you, ask him the questions, you may not hear the response, but I'm sure he will tell you.
I suggest you also speak to his wife, someone who can also feel the pain you are feeling, you both will be able to connect and share that grief and memory of your friend and her husband. Perhaps there is something neither of you are aware of; such as money trouble, you say your friend had a third child on the way. There are lots of reasons why someone would choose to leave by suicide. Don't put the blame on yourself, because you don't understand why and choose to get drunk and high as an excuse. Now it may hurt to hear this, but you need to sober up, and be proud of who your friend was, be strong for the memory of your friend and for his wife and children. All you need to know now is that your friend is at complete peace.
Stay strong.