There is no harm for a fasting person to taste food as needed. If they accidentally swallow it, there is no sin, and they can continue their fast.

Sujud Ash-Shukr is done in response to a calamity that is averted or a blessing which comes to a person. There is no specific du`a narrated in the hadiths for Sujud Ash-Shukr.

Your Sa`i between al-Safa and al-Marwah is valid, even if it was done without wudu because having wudu is not a condition of Sa`i.