If I do paid post and mention in my post that it is a sponsored post, how does google view this? Every big website and blog does this as far as I know. Further, if I use nofollow tag on links on my post will that keep me safe? I need to know this. What will happen if I openly reveal that it is a sponsored post?
Well mentioning that it is a sponsored review should not cause you any problem if you are using nofollow tag on links. If you don't use nofollow then Google might penalize you.
It would be best you let them know in advance, if your blog is good and you get good traffic then you can definitely pull this off.