Yeah, I don't really notice a difference in classic vs. novice modern sections, but the difference in riding a stockish twinshock is quite large. I love my TY due to a mix of nostalgia and the ability to enter any trial on it
As someone with a half metal leg, novice level trials has been fine - none of that jumping off big objects etc, and nothing more than bruises from coming off. If I were you I'd start out on something like a Gasgas Pro 250 - lighter than a 4 stroke (not a factor for riding, as much as a factor in pulling it out of funny places), pretty gentle power delivery, but with enough grunt to move you around - I started at 12 stone on a 125 and that was ok, 16 stone might make one struggle on a climb.
Good luck, I hope you enjoy trials as much as I do!