Below I have also attached some images of my wireframes, for any feedback on the meshes.
Very nice meshes, you clearly mastered edge flow.
Your wire frames look much better than the mesh would with materials on, I think that you should do some hand painting in Zbrush along the lines to emphasize the lines, so that there is a hint to the edge flow in the materials.
Iron man's arm looks like there was no consideration for anatomy, although as you verified it's a older model.
Only the light saber and Rifle look game ready. The race car is in need of cleaning, just removing and merging some edge loops, before use. Iron man needs a full retopology.
I think My main issue is that I don't fully understand what polygon budget would be used in certain situations. How high can you do with a 3rd Person Hero character, 3rd and 1st person weapons and environments filler props?
Poly budget changes per game type, however the idea is to use as little polygons you can while getting as smooth a model as you can.
Don't bother asking poly counts, remember that games made now are intended to be released in a few years time, who knows what it will be then.
The best way to get a poly budget for your model, is to rip a model from the newest top release in that genre, then add 25% to the poly count and use it as your budget.
One thing you will find from ripping models like this, is that games use a lot lower models than you would have expected.
A example is the The Witcher 3, most models average out 35 000 polygons, when they could have made them all at around 45 000. A other interesting thing is that Geralt sword's first LOD exceeded most buildings in polycount.