I think it is very smart of you to go for the 6x12 trailer. That trailer is a good size and should still give you room to put some extra stuff on, especially if you plan on staying with a walk behind mower. A 6x12 trailer is a size that really follows the truck nicely, meaning you won't have to take very wide turns...you probably won't really have to worry about turning with it actually. When you are backing up, learn to use your mirrors...you will thank yourself for it. It is much easier to back up a trailer using your mirrors once you get used to it. As far as what type of walk behind to get, a belt drive will be your best bet if you are working with a tight budget. I wouldn't be too picky on sizes, anywhere from 36"-48" should be fine. Get a name brand and one that appears to be in good condition. Best of luck to you.