Yep, it's easier just to buy the whole kit instead of just the shoes. This way you're also getting new spring hardware that's usually well rusted up, new electro magnets and the whole kit and kaboodle. Just eaiser IMO and the peace of mind knowing it's all new again and isn't likely going to fail.
Yep, you're prolly right about the 1500lb range for an 18ft landscape trailer. IIRC my 16ft utility tandem axle weighed right at 1000lbs. So 2 feet longer, then more metal for the cage, mesh, racks and gate you're prolly at the 1500 plus your gear but I'd still think just under the 2000lb range and brakes on 1 axle should be just fine for that. It's when you get into hauling heavy trucks is when you need to consider brakes on both axles.
This trailer only had brakes on 1 axle. It did fine for the 50 mile tow at 65mph, but the 3/4 ton Burb didn't have a motor or trans in it either and I could tell it would have made a difference to have the 2nd set of brakes if I needed a fast stop. Biggest part is knowing how to drive with heavier trailer. Allowing more space, don't be tailgating, and know how to use your brake controller manual braking feature if it starts to get squirlly back there. I've seen several people lose it with trailers. Once they start swaying, it's a bit touchy to get it back under control and the worse thing you can do is hit your towing vehicle brakes and put you right into a jackknife. Even brakes on 1 axle and a brake controller can get you out of the mess real quick no matter what the weight is, so at least have 1 axle with brakes if towing a vehicle.