Answer
(Fatwa: 1009/H=371/TH=1432)
(1) If one said takbir tahrima before imam, his salah with the imam will not start. However, if one advances during salah in saying takbir or in ruku or sajdah, then the salah shall be valid but it is makrooh to do so.
(2) Wudhu and salah shall be alright if no sign of drop was found on the body or clothes. But if you are certain that the drop discharged or seen, then you should make wudhu and re-offer salah after cleaning your body and clothes.
(3) If one loses one’s concentration during salah it does not invalidate the salah.
(4) Salah will not be valid if one recites the holy Quran loudly knowingly in a salah in which silent qirah is wajib and the salah shall be valid in which loud qirah is allowed. It is makrooh to develop the habit of saying takbir loudly, though it does not invalidate salah. The technique you adopted to rectify your tajweed is not right, you should stop it. Rather you should practice and learn tajweed with any expert Qari. After some time, your qirah shall be fine, in-sha-Allah.
(5) Sajdah sahv does not become wajib by repeating one ayat three or four times, but you should avoid it in future.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband