Next step in training?

So, I’m not sure as to what my next step should be. As you might know, I have a 15 hand 1300# Clydesdale/Haflinger/Percheron cross. Dam was a registered Clyde. Sire was 3/4 Haflinger and 1/4 Percheron. I bought him last fall I believe September-ish? Anywho, I’m debating on the next step. I haven’t done much with him this past year. I’d hoped to be driving him a few months back, but some things came up.
I have harnessed him (in my pleasure style harness) and done a ton of ground driving lessons in the safety of my round pen. Once we had a few lessons done, I ground drove him in my field as well as around my yard and out on the road. I have also “ponied” him along with my bomb proof trail horse. He’s been exposed to traffic and busier gravel roads now. I built a wooden travois (sp?) to get him used to pulling something and he didn’t have any issues even along the gravel with the noises it made. It also helped him get the “feel” of shafts alongside him. What should my next step be?
My older neighbor (in his 80s who has raised and trained Belgians his whole life) suggested taking him down to his place. He wants to hook him up to a metal breaking cart to teach him to pull and work in the shafts. It sounds like he wanted to hook him up and drive a truck or something in front of him? Maybe to avoid him running off? He thought this way we’d get him started right, and if he fusses a little, it won’t break the holy holly out of my antique wooden cart that I’ve spent the last 3 months restoring (off and on as a rainy day project).
My old 4H leader (when I was a kid) has 8 head of Clydes. She works them in a travois (like what I’ve done) and then puts them in an arena and slowly introduces them to the cart, then ground drives them with the cart. Eventually if all goes well, she hops in. What sounds like the best option?? He is a fairly mellow horse. I’ve hauled him along to horse shows and he is started under saddle, but still very green. I have ridden him in indoor and outdoor arenas. Both of these individuals have offered their help, and I know I can learn a ton from both of them, but more from my elderly neighbor. He farms with his drafts, which is eventually a goal of mine. He has a barn full of horse drawn equipment and still farms some of his land with his horses. Any opinions/ideas are appreciated!!