How long you been chopping for exactly?, you have already got the hang of perspective as all the c+p bodywork and bumpers fit well. Your smoothing has been done well and from what i see you have a good style with potential.
You will hear this alot when your a newbie but selections are sooo important, Whatever tool (lasso or pen) you use you should always have like 0.1/0.2 feather, it gives a clean edge to the selection and in the case of the lasso, mildly smooth out some jaged selection lines.
With wheels you should always get both the tyre and the wheel from the donor, this always leaves you with a better result as its alot easier to blend the tyre into the wheel arch than to merge the wheel onto the base cars tyre (if you get me, i aint a very good explainer, but i try

) i see you have done it to matiz and the first fiat, but not the other 2, oh yeah NEVER use the same wheel twice, the perspective will be wrong and when you try to make it fit, you will make the wheel look flat.
I see you shadowed the front wheel of the ford, looks good for a beginers attempt but its way too dark, try the brush at 0% hardness and around 10% opacity, the size is upto u and depends what your working on.
like i said you have some good beginers chops here and you got potential, just remember to take your time with things and practice tutorials on here and out there on the internet.
One thing i never see written or mentioned is
looking at real cars for reference, just simply look for pictures of cars on sites like flickr, hellaflush, modded car forums etc. with these you can see how the shadows form on wheels and anything else you want to see, and you can say right, "thats how it is in real life i will try make it look like that on my chop", also there are a few things like if your chopping a car in a studio background (i.e no reflections and artificial looking light, use donors with studio shots, the same goes for outside shots, there are different light sources and reflections etc. so outside donors should be used. I know its alot to read but I hope this helps ya mate, well done so far and i cant wait to see your progression.