Not sure were Reddogs is but if he is up north the steel deck trailers rust something horrid. Salt gets in between the deck and the cross members and wrecks havoc. What is the weight capacity of the current trailer are you using Red? I am surprised that it is struggling with your Kubota if it is a 7K trailer, it might be a distribution, or haul vehicle issue. I regularly haul a 5.5k tractor on a 7k 18' trailer with a 1/2 ton.
I hate metal decks. They are slick in the rain, freeze up faster in the cold, rust like crazy, and get dented easily. My experience with wood has been that if you use treated, or white oak they will last 20 years of use, unless parked under a tree or in the shade were they rot easy. I like to coat the boards in tongue oil, Linseed, or Thompson water sealer every few years.
If I buy a used trailer, I expect to just replace the entire wire harness, boards, and repaint it, however I also am not known for buying pretty stuff. But that is because I like to modify them to fit my need prior to repainting. Even when new from the factory the wire harnesses are not great, I had a friend who just bought a new PJ 24' 14K trailer and I expect that the harness will need replaced prior to the boards.
I would go with a wood deck. Without knowing your tow vehicle, budget, and storage plans it is hard to recomend a length, however I would go 18-24'. If your towing with a 1/2 ton with 10k tow capacity I would probably go with a 18' 7k , or 18'+ 10K. If your towing with a 3/4+ ton I would go with a 10-16K unit. Also I love galvanized trailers, they hold up great in the salt in the north.