Depends on how closely you work together. If you go for it and it doesn't work out, it can be really awkward having to see and speak to each other every day, but if you're in different departments, it's no such a big deal.
Yeah if its the wrong way.
having sex with someone you work with is fine but a relationship prolly not a good idea because you gotta see them everyday.
Probably, definitely yes! It would just cause to much drama and ickiness in the workplace. Keep your fantasies to yourself.
It depends on your office policy. I've worked in places where they frowned upon it but they didn't intervine. I've also worked in offices where they would dismiss you for inner office romance.
I have dated people I worked with an although initially it was wonderful (it made me excited to go to work) when things turn sour it is the WORST!