Whoever gives iftar to one who is fasting will have a reward like his, without that detracting from the reward of the fasting person in the slightest.

It is permissible to swallow the saliva after using the siwak while fasting, but if anything comes out of the siwak in the mouth, you should spit it out

There is no reward for delaying breaking the fast, rather it is better to hasten to break the fast as soon as the sun has set; this brings a more complete reward.

The Sunnah is to hasten to break the fast, which means breaking fast straight after the sun has set. For more, please see the detailed answer.

Du`a for breaking fast should be made before iftar, at Maghrib, because this combines weakness and humility, and because he is still fasting.