Tithing truly does take great faith. Simply place your trust in God. If you wait until you feel that you are financially comfortable you will never take the step. The commercialism of our society works to convince us that we never have enough. No matter how much we have, there is always something else we will want. If you are ever going to tithe, you will have to step back from your endless list of wants and believe that our generous and abundant God will always provide you with all that you need and even with enough to give back a generous share.
“He who did not spare his own Son but handed him over for us all, how will he not also give us everything else along with him?” - Romans 8:32
No. Tithing is specifically giving back to God through your church. Therefore, giving to other charities does not constitute as tithing to your church. Tithing is also something that you give without getting anything in exchange, that is why paying private school tuition (catholic or any private school) also does not count as tithing to your church.
Here is an easy formula for determining your tithe to your parish.
“Then he said to the crowd, ‘Take care to guard against all greed, for though one may be rich, one’s life does not consist of possessions.’” - Luke 12:15