First of all, apologize and said that you have something very urgent to attend to and that you would love to reschedule the date. Let the other party propose a date/ time and make sure this time you can attend with no prob

Rescheduling with a valid reason will not give a bad impression. There are times when certain issues are urgent and last min. If the company is understanding, they will be willing to meet you at another date.

"tell me about yourself"

just give a general overview of ur characteristic like outgoing, cheery or such... can adapt well to new things, all that textbook answers. its a formality and interviewer also probably not listen to what u say but how u say it.

I was asked "How many interviews have you gone through by far?" for one of my interview last year. I merely told the truth and I think it's best to be honest if we can.

And I replied them that I went through 3 that week (theirs being the 3rd). Then they asked whether I received any offer and I said, yes, one of them (which was indeed the truth). So with that, they tried to get out of me which company that offered me the job but I gave them vague answers and whatever I could answer (eg. location in xxx).

I was selected for the 2nd round but decided to go with the other company's offer XD

In any case, IF you have applied for 10 companies for the last 2 weeks, it would be better to say that you applied for 5. Do not make an impression that you are desperate.