No. Moto Z2 Play is not CDMA+GSM. It is GSM+GSM.
Yes, it does support OTG.
Yes, with the help of MicroSD card, you can expand the storage up to 2 TB.
No. Moto Z2 Play does not support CDMA network.
You will get one Style Mod free but you have to buy Camera mod, Battery mod, etc. if you want them.