Please help me correct my english grammar below.

Dear Sir,

Good day, thank you again for your effort in helping me to hire and working back in the company it would be a great gratitude to you.
TO pay you back i would do my best to work hard and contribute a skills for company's benefits. I would keep my honesty and trustworthy towards the company.

Sir, i would like to inform you in advance that this coming march 2019, I would like to take a vacation for 30 days only.

thank you for your kind hearted person understanding and i really appreciate you always.

thank you and best regards.

Thank you for hiring me. I am looking forward to working for your company.

I will do my best to work hard and contribute my skills for company's benefit. (I would keep my honesty and trustworthy towards the company. UNNECESSARY. THIS IS ASSUMED.)

Sir, i would like to inform you in advance that this coming march 2019, I would like to take a vacation for 30 days only. (AS A NEW HIRE, IT IS NOT ADVISABLE TO IMMEDIATELY ASK FOR TIME OFF.)

(thank you for your kind hearted person understanding and i really appreciate you always. REDUNDANT AND UNNECESSARY.)

Thank you and best regards.

Dear Sir,

Good day. Thank you once again for your efforts in helping me to be hired and for allowing me to work back in the company. I am extremely grateful to you.

To pay you back, I will do my best to work hard and contribute my skills for the benefit of the company. I will maintain my honesty and trustworthiness towards the company.

Sir, I would like to inform you in advance that I will be taking a 30-day vacation in March 2019.

Thank you for your understanding and kind-heartedness. I truly appreciate everything you do.

Thank you and best regards.