Tipping Vendors

Hi, I'm saving for my vendors and also want to account for tipping so I have enough money by the wedding day. What do you tip for the vendors - limo, dj, photographer? I don't want to give too much or too little. I'm not even sure who I have to tip - do you tip the waitstaff and maitre'd in addition to the 20% the reception hall is charging? Any help would be greatly appreciated!!! Thanks