is there any possible conflict for fields with the same machine name?
Machine names for fields must be unique per entity type.

The means that with nodes, fields must be unique across all content types. So you can't create two fields with the same machine name on different content types, as both content types are nodes, and machine names must be unique for the entity type. (Edit - you can however re-use the same field on multiple content types, but it will be the same field, not two fields with the same machine name).

You can have a field_image on a node, and field_image on a taxonomy term. Here, the machine name is the same, but unique to each entity type, so there is no problem.