My venue is already taking care of the catering so I didn't have to worry about that anymore. Ask your venue if they have preferred caterers. Some venues are strict with this so make sure you check with them first.
The catering is probably something I'd put over the DJ but there has been some debate between me and my parents on what will be served so I have been trying to respect their opinion. I'd start by booking the most expensive and important things to you. Photos are VERY important to me so that was immediate after the venue. Bar came next because our guests are Czech/German and like to drink. Do what suits you!
Well i’d say the first thing is to have a number margin of the guest list. you can’t really book most vendors without them asking for a guest count. then i’d say try to book the vendors and try on dresses and such.