Consider a different strategy of planting a few extras and pulling all during the first harvest. Derby, Tema, Bronco, Strike and many others tend to set most of their beans uniformly. I find that I can sit on a cart and pull and pick 2 rows making much better progress than if I try to just find beans on the inground plant. Always have a backup planting to move onto and you will avoid those overmature missed beans and poorer followup pickings from the same plants. The ease of picking is the greatest benefit from pulling plants. If you hold the plant on its side most of the beans will hang unobstructed so you gan grab a handfull at once. Then by twirling the stem the remainder of beans are easy to access. It's so easy that I do the vast majority of my bean picking after dark with a headlamp. My harvest rate is better than during daylight hours and beans are more crisp.

I concur with Fusion's recommendations for bush bean spacing. The 20-36" spacing between rows is dependent to a large extent upon the variety - some sprawl more than others. In my irrigated garden, 24" between rows usually works for me. Only a few varieties - such as some of the bush Romanos, like "Jumbo" - need more than that. It depends, too, on how much of a path you need. Most of my beans are pole... but I generally grow 1 or 2 bush varieties each year, usually for shelly or dry use. My yield for bush beans has been 1-2 ounces/plant dry seed, at 6" spacing. This is considerably less per plant than pole beans; but since you can space the plants & rows more closely, the difference is not as great as it might appear to be. For large areas, due to the wider row spacing required by pole beans, the yield per square foot for bush beans can exceed that of pole beans. I would count on a pound of dry seed per each 15 feet of row, at 6" spacing. Well cared for, on good garden soil, you could get twice that. As Fusion mentioned, pole bean yields can be much higher - per plant. In the "Bean Science" thread, I linked to a discussion where I gave the yield per plant for the pole beans I grew last year. Best case scenario, I have had single pole bean plants yield nearly a pound of seed. These were very widely spaced (due to a poor stand) but the results were spectacular nonetheless, and showed what pole beans are capable of under ideal conditions. At 12" between plants (my default spacing for most large-seeded pole beans) I typically get 6-8 ounces per plant. Since I generally lose a percentage to spoilage each year (from late summer rains & frost), these figures are fairly conservative. Don't know about your climate in late summer, Tsctoehr, but if all of the pods which set are able to ripen before frost under dry conditions, 8 ounces per plant (at 12" spacing) should be a reasonable expectation. That is for beans intended for dry use; snap beans with their smaller seeds may yield less. Realistically, I would count on using a 30-foot row for a gallon of dry beans... but with a little TLC, you can get better than that. One pole variety gave me 7 pounds from a 20 foot row last year... and the last pods were lost to frost. If space is limited, you can best take advantage of pole beans' superior yield by planting a single row on the North side of the garden/bed, where they will not shade shorter plants. Since we are discussing both weight & volume in regard to yield, I wanted to get a conversion factor. Measuring several of my dry beans, their net weight was between 7-8 pounds/gallon. Keeping in mind that dry beans expand when cooked, a gallon is a lot of beans. As for crossing between common beans (Phaseolus vulgaris)... like Fusion, I have personally experienced very little. When I grew pole beans in adjacent rows, I had some crossing, maybe 5% or less. I grow them at least 30-40 feet apart now, with barrier crops (flowers & flowering vegetables) between them, and almost never get a cross. However, I have received severely crossed bean seed in trade - one ("Jeminez") nearly 100% - so I know it can occur under the right conditions.

In my bush bean patch, I noticed I have a few really heavy producers, and they are the ones growing next to a "bare spot" where I had to pull a diseased seedling, or at the end of the row. It makes me think I should give them all more space next time. Exposure to sunlight from top to bottom may be the key, I don't know. Mine were planted about 5 inches apart.

The Fortex set pods for me non-stop... they were ready in droves from beginning to end of the season (right about now they are just about done.) Whereas the bush beans just had one drove that wasn't really any bigger than the Fortex first pickings, they did produce continually but no comparison to the pole. Just my experience... they definitely were a lot more work, setting up poles for them to climb and training them up. But they were also so much easier to harvest, picking the bush beans was a real pain with them planted way too close together.