If you're Christian and you believe in god and you commit suicide because someone was majorly bullying you or something then most likely yes you will go to heaven but if you did it just because you feel like it then most likely not. It all depends on many factors. God judges you after you die so it's all just his opinion and no one knows his opinion. If you commit suicide to save someone's life, for instance taking the bullet for someone or cover a grenade, then you definitely will go to heaven.
Really the truth of the matter over the salvation issues on suicide & homosexuality are in scripture. It says do not say in your heart "Who will ascend into heaven or who will descend into the abyss". God has appointed a righteous judge.
No. Theyll go to hell if they didnt know God before they died but it is not an unforgivable sin for a believer. It IS a sin and one youll have have to answer for, but not unforgivable. Youll just have to explain to God why you took matters into your own hands and committed such a sin instead of trusting Him to be your support.