Yes, Redmi Y2 does have the support for Miracast.
No. Redmi Y2 can support only one 4G sim card at a time. Another sim card will work either on 2G or 3G network as per your preference.
Yes, Redmi Y2 does have the dual app support.
Yes, Redmi Y2 does have a dedicated MicroSD card slot. You can use 2 sim cards and a memory card at the same time.
The Xiaomi Redmi Y2 is a slightly better attempt at a selfie-focused smartphone than the model it replaces. It has proven hardware that is capable of delivering a smooth user experience, plus MIUI 9.5 which has a lot of added features.