After you trim and clean the flash off the metal parts, give them a wash with warm soapy water, and then rinse them with warm clean water (no soapy residue). If the metal seems to lose its luster, that is okay!
I agree with Invisible Officer. For metal and metal+resin figures, use a good cyanoacrylate glue (superglue, Krazyglue, Hotstuff, and so on) to attach the bits. But be careful. There is a technique and not all CA glues are the same. Also, a toothpick can come in handy at times for applying the CA glue.
For attaching larger bits, you might consider “pinning”. Pinning is basically drilling small holes and using pins and CA glue for better strength and durability.
For filling noticeable gaps or imperfections, you can use a good epoxy putty.
After you finish assembling your metal figures, and after the glue and any epoxy has completely set, wash the figures again to remove any oily finger prints and other residues. BTW, this also applies to plastic figures/models as well.
After the metal figures are fully dry, I recommend using a good spray metal primer. A quick thin coat is all you need. Don’t worry about every tiny nook and cranny, and over spray is bad. Most metal primers come in light gray (which is good), but now you can get some special army colors (I have not tried). Floquil Paints use to make one of the best metal primers, but I have not tried Floquil’s new formula. Tamiya, Hobby Boss, and Testors also make good metal primers. I also hear good things about Vallejo’s surface primers, but I have not tried them yet.
Priming Plastics?
For metal figures, I think priming figures with a good metal primer is almost a must. For plastic figures, you do not have to prime the figures! Yes, I said it. However, this a long and detailed topic (and controversial by some) for another time.
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