That is plenty of MG/MF vine plants, in fact if you really think you want them entwining with your veggies you could thin them out significantly. One plant of each will suffice. Six or eight are already too many for a 4' wide arch.

Personally, I would not plant these particular flowering vines with my cukes and beans. They will tangle up in your veggie vines and definitely compete for light,water and nutrients.

Here is your answer. I don't know how many MG germinated but it was enough to significantly suppress beans (red scarlet). But it looked nice and, after all, how much beans can you eat...
{{gwi:686603}}

Once you plant morning glories you will never have to plant them again :) I have been spending the last month on morning glory patrol trying to keep them out of a "cottage" type bed I have. Every year the morning glories and the wild morning glories/bindweed? takes over that bed. I'm giving it one more year with diligent m/g patrol to see if I can get that bed to succeed without being choked to death. If not, that bed will need to be rethought.

I do let them grow on my fences, in spots.

Wow - thanks for the advice and pics. I will thin them down to one flowering vine per arch and see how it goes. I want it to look good, but I really want to eat the beans and cucumbers!

Lisa, I grew Heavenly Blues one year and they never returned. I do get volunteers from the moonflower vine.

Like everything else with gardening, It Depends.
Vigilance is the watchword of the day. Morning glories grow very, very, very rapidly. My husband used to joke that if we left the windows open at night, we'd find them winding around our toes by dawn.
They also self-seed with abandon. Even if you thin them down to a single vine, offspring will show up unbidden in other parts of your garden.
Kay