1) Your run looks more than secure enough to allow your birds free access to it during the day
2) A pop door is simply a small door (usually around 14 x 12") for your chickens, usually leading from the coop to the run. It's nice in winter because it allows less cold air in during winters...
3) Your coop run probably does seem roomy now, because your chicks are babies. But when they're grown to the size of house cats...well...can you imagine 25 house cats living in that space??? As was pointed out, most folks try to give their chickens a minimum of about 14 sq. ft of space each (4 sq. ft indoors/10 sq. ft. outdoors); your birds currently only have about 5 sq. ft. each TOTAL. You have a high likelyhood of problems developing, especially as your birds mature, and especially when cold weather hits. You might want to consider downsizing your flock enough to give them appropriate space. Do you have the room to expand your run to about 250 sq. ft (you now have 64 sq. ft)???
2) A pop door is simply a small door (usually around 14 x 12") for your chickens, usually leading from the coop to the run. It's nice in winter because it allows less cold air in during winters...
3) Your coop run probably does seem roomy now, because your chicks are babies. But when they're grown to the size of house cats...well...can you imagine 25 house cats living in that space??? As was pointed out, most folks try to give their chickens a minimum of about 14 sq. ft of space each (4 sq. ft indoors/10 sq. ft. outdoors); your birds currently only have about 5 sq. ft. each TOTAL. You have a high likelyhood of problems developing, especially as your birds mature, and especially when cold weather hits. You might want to consider downsizing your flock enough to give them appropriate space. Do you have the room to expand your run to about 250 sq. ft (you now have 64 sq. ft)???