Concentration in Salaah (Khushoo' and Khudhoo')

Q: Is it permissible to picture that one is standing in front of the Roza-Mubarak when reciting Durood Shareef in Salaah?

Q: I am 72 years old and I have a problem with concentrating in namaaz. I know it is not permissible to read namaaz with your eyes closed but at the moment I concentrate better with my eyes closed. Please advise me how to overcome this problem.

Q: Does thinking of worldly things while in prayer makes the prayer invalid? How do I know that my prayers are being accepted?

Q: I have read somewhere that it is makrooh to pray near impurities. Is it makrooh if one prays in a room that has a toilet attached to it?

Q: I have read somewhere (I think it was Baheshti Zewar) that it is makrooh to pray in a place where one would get distracted. What is meant by being 'distracted' in this ruling?

Q: What is the meaning of khushoo and khuzoo in salaah and how do we attain khushoo and khuzoo?

Q: What is an easy way to acquire concentration in salaah? When I start offering salaah, then mundane affairs and other things come into my  mind and distract me. 

Q: How does one humble oneself in salaah?

Q: I pray all my salaah but most of the time when I read salaah there is no concentration (jamaat or alone). I don't know whether my salaah is accepted or not and I also get bad doubts.

Q: How to attain khushoo and khudhoo permanently in salaah despite having doubts all the time?