Having fear in the heart is a blessing, inshallah. As for the questions you have asked, one simple answer cannot be sufficient as it has many queries. Instead of trying to provide a separate answer for each question you have asked, I believe a holistic approach would be better.
The first and foremost thing we must understand is that,
Narrated 'Umar bin Al-Khattab : I heard Allah's Messenger (ﷺ) saying, "The reward of deeds depends upon the intentions and every person will get the reward according to what he has intended".(bukhari)
And with that, we have to remember ;
On the authority of Ibn Abbas (may Allah be pleased with him), that the Messenger of Allah (peace and blessings of Allah be upon him) said : Verily Allah has pardoned [or been lenient with] for me my ummah: their mistakes, their forgetfulness, and that which they have been forced to do under duress. (Ibn majah & nawawi)
No one would know better what is your intention than Allah azzawajjal and yourself. So do not be discouraged with such doubts, it's just Satan trying to distant you from worship.
Minor shirk (shirk ar-riya) is something which we have to be very vigilant about. Always make your intentions pure and try to do the best you can only for your Rabb.
Regarding ostentation in worship, it is reported in Al-adab Al-mufrad (715) ;
Ma’qil ibn Yasar reported: I departed with Abu Bakr to meet the Prophet, peace and blessings be upon him, and the Prophet said, “O Abu Bakr, there is idolatry among you more hidden than the crawling of an ant.” Abu Bakr said, “Is there idolatry other than to make another god alongside Allah?” The Prophet said, “By one in whose hand is my soul, there is idolatry more hidden than the crawling of an ant. Shall I not tell you something to say to rid you of it both minor and major? Say: O Allah, I seek refuge in you that I associate partners with you while I know, and I seek your forgiveness for what I do not know.” (graded sahih by Al-Albani)
So be firm in faith. There are reports that even the companions feared that their prayers might not be good enough but that never stopped them, it only made them work harder to do better. And always remember what Allah azzawajjal said ;
Say, "O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful."(39:53)
So fear Allah azzawajjal as much as you can and hope for His mercy always and continue in worshipping Him.
[ Note : as for making your recitation good avoiding ostentation, I think the best way would be just recite to please your Rabb, no one else.]
May Allah the mighty and sublime grant us mercy and guide us to the straight path.
Allah knows best