What should I do regarding my recurring doubt about the number of prostrations and bowing units, and about the takbir and tashahhud during prayer, and the resulting re-performance of prayers or dissatisfaction with their performance, in addition to my suffering from difficulty in forming the intention for ablution and prayer? Is it a condition to precisely articulate the letters during prayer, or is moving the lips sufficient, knowing that these whisperings began with doubt about purification from urine?

The cure for whisperings (waswas (definition)) is to disregard them and pay no attention to them. If you intend to pray, do not hesitate regarding the intention. Rather, bring to mind with your heart the prayer you wish to perform, then say the opening takbir without hesitation. Whatever doubt occurs to you during your prayer, do not pay attention to it unless you are certain that you have abandoned something. As for pronouncing the letters, it is obligatory to pronounce them from their proper articulation points while avoiding waswas and excessive doubt in pronunciation.