NICE DUCK! One of my long-fav vehicles, but I've yet to add it to my stash of stuff I won't live long enough to get to!
I DO think those roadwheels are maybe a little stark, but...
IMO, leaving tire seams on would be realistic, as this would have been both a late war production and low-mileage. Looking at various Pz. IV pics suggests to me that those tires were pretty hard rubber and that those mold seams did linger for quite a while.
Of course, getting a show judge to recognize this is another matter altogether. (So, being an old chicken, the Pz. I've done and shown have all had smooth tires )
About spare tracks and camo... Personally, I think your camo'd picket fence looks pretty snazzy! In the (then) real German world, that fence COULD have been camo'd, specially in later 1943 and thru 1944, as field crews often did the camo in the field over the factory base-coat, and as seen in many pics often did spray the tools and spare tracks when doing their in-field camo thing.
The question probably would be whether the spare tracks were base-coated when assembled on to the vehicle at the factory or rear depot... IF so, then it would be reasonable to use all 3 colors on those tracks (that is, continuing the hull scheme over the tracks). IF NOT, then they may have started mounted life in either a naked (slightly surface-rusted) steel, or maybe in rotoxid primer or maybe in black enamel....
And from there, IF the crew did the "continue spraying camo over spare tracks" thing, than it may well be fair to use one of those colors (rusted steel, enamel black, rotoxid?) as the base on the tracks and carry the camo colors over that!
I'd bet that the tracks left the factory in naked steel or black (or sometimes the rotoxid) - not in the dunkelgelb base-coat, so...
Nice job (even if, yes, you did leave a little seam on that barrel - bet that was both hard and low-mileage, too! )
Bob