Newbie here with some questions about my cycling tank

[Jfish]

It is possible to cycle with fish however it is frowned upon because when the ammonia, nitrite and nitrate levels rise it becomes stressful for the fish. They are hardy fish and may appear healthy now but after several weeks of unfavorable levels they may start to stress.
Im not 100% sure on adding mature water from other systems so i'll let someone else help ya with that one. I guess it could contain some beneficial bacteria however it could also include other nasties you dont want to add to your system.