Enjoy your questions and comments on here, good luck. With the progress. Be careful, these are crazy times, reminds me of the 1970s, things are different but also the same, the 1980s were not as much fun and a lot less neighbors after that settled out.
Friend of mine has a 8 row 7000 for corn, with a modified 7 (was 8) row 7100 that attaches behind it on a 2 frame cart. Makes 15 inch bean rows. Kinda slick, but after a number of years he"s wondering if it.s worth hooking off and on all the time. The 30 bean rows aren"t bad here if you pick the right bean.
I"ve seen other setups, but always with the extra units on behind.
If you want to try 15 beans, get a slow down gear for your planter, and double-plant. Some offset the hitch and just come back in the same tractor tire tracks, others like to plant in aid and pattern, say there is less sprayer damage and easier combining with the criss-cross demand pattern.