you should be able to grow 4-6 plants in a five gallon bucket.

if growing on the fire escape, you should be ready to bring that bucket in at a moment's notice. most cities have ordinances about blocking fire escapes - safety issues. but you might get away with it, as long as no one complains ....

I know there's a few varities of Sugar Snaps (the most popular one here is Oregon Sugar Pod II) that only get at most 30" high, and you can easily grow 6 plants in a 5 gal. bucket, with only a 32" tomato cage to hold them up. I did two of those last year, and they came out great.

As for the fire escape thing, probably not the best idea. Best case scenario, you're asked to remove them. Worst: aside from being slapped with a fine, you could end up putting someone in danger by putting obstacles in an escape route. There's a good chance you or someone else may never use that escape, but that's chance for you.

I have sowed the seeds of 60 cm tall green peas for the first time in my life on the balcony this year. I have the container that is 75 cm long, 31 cm high, 29 cm deep. I've sown three rows of peas with 5 cm distance between them in a row and with 5 cn distance between the rows. One month has passed already and all of the seeds have sprouted and now they are about 20-25 cm tall. So they are growing, hope that I will get a rich harvest.

I had a 20" deck box for my peas, and planted two rows, with a support down the middle. Maybe I could have done 4 rows, but I didn't want to push it. Anyway, the results were tasty, but not enough to do again next year. In two harvests combined I got enough peas for one serving. Perhaps I'll use the tall kind next year, and see if I get a bigger crop.