Consider the Timing
The party can be more easily managed if you think of it in terms of sub-events which should help you to keep your sanity. By this I mean items like:
Setup Time - You may want to have some games & distractions so you and your entertainment can setup for this wonderful event. Several friends/assistants may be helpful with this item
Arrival Time - For guests, consider allowing for at least 30 min for arrival times since not everyone is on-time. For Entertainment Act(s), will you have multiple entertainers and if so will they be performing at the same time? Consider the time they need to setup and tear down as well.
Food - Will it be before or after the entertainment? It is recommended that the food be after the entertainment especially if you have a magician. Sticky fingers and volunteering to handle expensive props are not a good idea. Also, consider having easy cleanup finger food.
Entertainment Time - How much time are you allowing for entertainment? Will you have multiple types of entertainment? A lot of clients like to have a magic show and then balloons or face painting. It takes time to switch from one to the other unless you are paying for multiple entertainers which is usually pricey. Usually it is desirable from a pure dollars standpoint to hire a single entertainer who can provide all the services you need.
Cutting the Cake - This usually works best right after the entertainment. They can pack up without little fingers getting in the way.
Present Opening - This usually works best after the eating of the cake. They are full and are ready to sit for awhile.