Awesome job on the armor and weapons. Reading some of the previous posts it seems you have a problem with paint to keep foam smooth.
Now as a modeler of airplanes and tanks I can give you some advice on how to solve this, if you are willing to spend some money that is.
Buy an airbrush and a compressor. Since it is likely your first time using one get a cheap one. This one is good.
Choose your paints. You probably know that Acrylics are all that will work on foam, so you need to buy airbrush acrylic paints. There are tons of these and it comes down to personal preference. They can be sort of expensive though.
To prime or not to prime. With foam (I'm assuming you use the pink foam) you really don't need to prime if you use an airbrush, but you can anyways if you want to pre-shade or something. Make sure it is a latex primer.
Learn to use the airbrush. Don't just wing it, practice some first.
The two biggest advantages to this method are the paint layers is extremely thin and all the details pop out if done right. Once you get good at it the method can also be very accurate for some details.
Good luck on your next project. I'm sure it will look good regardless of how you paint it.