It's difficult to know what size or type of dump trailer you will need when you are planning to do many different types of work with it. It is best to write down all the different things you want to accomplish with it such as collecting debris to be taken to the dump, hauling dirt for landscaping, hauling cedar chips for landscaping,etc. Think about how much room you are going to need for these tasks.
Ask yourself what types of vehicles do you have that can pull a dump trailer, what is their hauling capacity. Look in the owners manual for each vehicle to be sure. These are all questions you need to answer for yourself before shopping around for a dump trailer or a trailer of any kind.
After you have these questions answered it is a good idea to call around to many different manufacturer of dump trailers to see which ones take the time to answer your questions. Are they pushy and try to rush you into purchasing a certain model without listening to you or do they truly take the time to listen to your concerns? Are they pleasant even after you tell them you will get back to them later? A good salesperson never closes the door but leaves it open to future possibilities.