Role Playing with my boyfriend?

well i would suggest you find him doing some kind of crime (even a silly one like watching porn) and then ether try to cuff him or let him "fight" back and cuff you then basically whoever is not cuffed rapes and uses the other person (if your cuffed you should be ready to give oral as should he) maybe after one if you uses the other they "escapes" and uses the other person

anyway have fun with your boy ....dont lose the key

Ummm do you really need to know? Why don't you stop by my house first and I'll show you

I suggest you wait till you get there to change into the costume. Too many things can happen on the way to his place. A traffic jam, and accident, or just a flat tire, or running out of gas. One never knows.
As to the handcuffs, that will depend on just how kinky you two want to get.
As you're the cop, you can handcuff his wrists behind his back, after he's naked, ( no sense in doing it while he's fully clothed, as you would then have to remove him ) Then he should be on his knees, begging for you not to arrest him, and then just use your imagination as to what you want him to do to please you.
You may need to find out, if he's submissive and if you're a Domme, try and work out some scene in advance that you can both agree on. It'll at least start you off in a good way. Then you can just wing it from there.

lol u thought of the whole plan
but u don't know what to do...

what do u think handcuffs r for? lol
let him cuff you so he can take control or vice versa