The Du`a ‘Allahumma laka sumtu was ‘ala rizqika aftartu’ is narrated in an inauthentic Hadith. There is no source for the Du`a ‘Ashhadu an la ilaha ill-Allah astaghfir Allah as’aluka al-jannah wa a’udhu bika min an-nar.’ The reported Du`a when breaking the fast is ‘Dhahaba ath-Thama’u, wa abtallat al-`urooq wa thabata al-ajr insha Allah.’

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.