These are awesome models, the vehicles are especially cool because they have a lot of Orky feel and character. The art of marking something look badly (Orky) made but not be badly made is quite a tricky feat and you have managed it really well.
Skin tones are great, as mentioned by many commentators before, as is the rest of the painting. Clean, neat and convincing. Was really amused by Mordheimer's comments: drilled gun barrels, painted bases, as neither of these things bothers me all that much. What does bother me is the ejector ports on bolt weaponry, which is meant to fire case less ammunition!
Bumper is exactly the right word, but there isn't a specific name for soldering "tin", rather in English it is just called solder (apparently). Spanish and Dutch do have some similarities, as they are both Indo-European languages - its really hard to learn Swedish because it is so like Dutch and I keep getting confused.