Hello, Ricihe!
>1) Is this a same number of questions with real TOEFL?
They said in the bulletin that the number of questions can vary, but I got as many questions as it was in POWERPEP.
>2) I got a score 06-25 from Structure section, how many I missed? (Total q:20)
The section isn't computer-adaptive, and we assume that every right answer costs about the same. I'd say you did 5-7 wrong.
>3) Is POWERPREP harder than the actual toefl(I heard before)?
Not really. Anyhow, think optimistically :).