I love restoring old implements as much as I do reworking old tractors. I'm just finishing a 2-row cultivator. It was a rust-ball when I started. My plow I use for the garden was much the same way. I've done a couple 2-row planters also.
Start by dismantling them. Take a wire wheel (on a 4-1/2" grinder ?) to as much as you can, and/or sandblast. Straighten parts that are bent. Replace (if possible) any parts that are too badly damaged. I like to prime and paint while everything is apart. Re-assemble, and shoot a final coat of paint. Decals are available for most John Deere (as that is what I have experience with) equipment, and I'd assume they're available for other brands also. (I get MOST of my decals through K&K TRACTOR, in Shelbyville, Indiana)
There's a great deal of satisfaction in restoring anything old. Add to that, there's a great many older implements that just aren't available new anymore (i.e. plows...)
As soon as I get the bugs worked out, and can post pictures on here, I've got several completed projects I'd like to show off. Plows, a disc, a couple 2-row planters, cultivators, a baler, even an old pull-type Deere combine.
And half the "fun" is the search for replacement parts for all the old stuff....