What is the difference between the Cisco and Juniper interfaces, what command/query differences do we need to keep in mind?

1st thing both are linux based os. Commands and interfaces are some how the same. As juniper ia following the foot steps of cisco. Like in cisco sh vera. Junipwr also sh ver. Cisco sh ip route juniper sh route. Etc

Yes, You can use Junos Olive in GNS3.

do we have any simulation software like the packet tracer proprietary of Cisco, for Juniper?