"Funnily enough, I do believe in democracy". [my sentence]
"Funnily enough, he did say he believed in democracy". [my sentence]
funnily enough is an idiomatic expression that means that what you say after it is unexpected. It can be placed at the beginning or at the end of a sentence, and not usually in the middle. It is more spoken than written. It is ...
No. The adjective is correct.
"the amount of time that young people spend inactive."
means "the amount of time that young people spend as a result of being inactive."
This use of adjectives has two categories:
I shot him dead = I shot him [and, as a result, he was] dead.
No, "inactively" doesn't work here. This is what the relative clause says:
Young people spend X amount of time inactive.
Which could be read along these lines:
Young people are inactive for X hours a day on average.
The adjective "inactive" says something about the subject "young people".
Ago works well here. It retains some of the nuance of time and can only really be replaced by "earlier" - which would refer to earlier in my journey which is neutral as to whether it means "at an earlier point", or "at an earlier time."