Place all the frames in the middle of your hive bodies (centered)-all the extra space will be on the two sides. It will over time get some burr comb but nothing to worry with or about.
As far as paint, most beeks here are all about a good deal, so basically anything that you can find at a home improvement center's mistint paint section works great. I started out with white latex, now I have some greens, some pinks, etc. Its all basically up to you, just be sure to paint the outside faces only-leave the insides bare.
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