Have you got driving experience? If not, it certainly doesn't hurt to get some, and spend a while ground driving. My barn owner taught me to drive their Saddlebred mare before I got my Haflinger. Took me a while to get his harness from the time I bought him (almost 4 years), but he'd already had training as a carriage horse. I spent 3 months ground driving him, which was more for my sake than his, before we hooked to the cart.
As far as nylon harnesses go, I don't think there's a lot of good ones out there. The ones I've seen on horse.com and stuff look cheap and poorly put together, and they're just a felt pad with no real tree on the saddle. No bueno! That said, before I got my Comfy Fit betathane harness, I drove in a Liberty harness from Amber Hillside in Canada. It cost me around $200, with shipping, and I think as far as basic starter harnesses go, it's way better than the Tough 1 harness or anything of the same ilk. There's a real tree to the saddle, and it's well made by a real harness shop in the same way their leather harnesses are made. After I placed my order, I was asked for my horse's measurements so they could mix and match if they had to, and it fits my 14.1 hand Haflinger pretty well. Nylon does need to be kept fairly clean, but it's just a matter of scrubbing it, and letting it dry in the sun, and the harness itself is vinyl-lined on the breastcollar, neck strap, saddle and breeching so those parts that touch the horse can be wiped off more often. Amber Hillside Horse Harness - Formerly Rons Horse Harness - Liberty Harness
It's a decent harness, in my opinion, especially when one's just starting out. I'm not fond of leather harnesses because it's so dusty out here that I just like being able to wipe my harnesses off without having to do a lot of work keeping them clean. And it takes a lot to keep leather clean, which is why I got the Comfy Fit after I knew I was going to be a lot more serious about driving, but the Liberty nylon harness was what got me started, and I still keep it as my spare harness (as well as the one my mare is being ground driven in)