As you mentioned the Halachos are very complex, so I will be a little vague in my answers for the sake of brevity.
1) It is a machlokes, but generally accepted as something that must be done when one is obligated according to Halacha.
2) If giving ma'aser would prevent one from paying a loan he owes, the loan has priority.
3) Someone who cannot afford basic necessities may be exempt from the mitzva of Ma'aser Kesafim.
In all these issues your Rav must be consulted regarding specific Halacha l'Maaseh.