Is it obligatory to continue building upon the most (likely number of units performed) in prayer when doubts about Al-Fatiha, Takbir, or Tasbih recur daily, or is there another solution?

Your construction is mostly correct, so do not pay attention to whispers (waswas) and pangs of conscience; because you based your action on the answer of the people of knowledge, whom we have been commanded to ask. You are a doer of good and there is nothing upon you as long as you have done what you were commanded to do. We advise you not to pay attention to whispers (waswas) and not to make up (the prayer), for caution is good as long as it does not lead to contradicting the Sunnah. Whoever is afflicted with whispers (waswas) must do two things: frequently remember Allah, supplicate, and seek refuge (with Allah), and connect with a student of knowledge or a shaykh and act upon his fatwa without paying attention to anything else, and accept the fatwa with an open heart.