Thoughts on no copay, referral for everything plan?

I’m late 20s and live in NYC. I have a PCP and a gastroenterologist that I see a few times a year. I’m in good health. I want to start seeing a therapist. I work for the NYC DOE and have 2 free insurance options — GHI and HIP HMO. The GHI has copays without referrals, and the HIP HMO has no copays with referrals for everything. Do you have to make an appointment with your PCP every time you need a referral, or can I just request one over the phone? If she already gave me a referral to my gastroenterologist on my last insurance, will I need to request a new one? Can I get a referral for therapy? Do referrals expire? Do you need referrals for procedures too? I need a colonoscopy — would I need a separate referral and have to wait for insurance to process it? I see all my doctors through Summit Health Group, which accepts HIP, would I be so crazy to do HIP HMO? Everyone seems to say avoid it, but I don’t fully get why. There’s not much information about any of the plans online, sorry for all the questions.