I think you are asking if there are any limitations or restrictions in terms of basic functionality between MongoDB Enterprise and the community/OSS version. The answer is no - there is no difference or restriction in terms of the amount of memory, storage or number of instances/sets/clusters you can run using the OSS version, nor is there any difference in the failover mechanics between the two.
The differences (as listed on the MongoDB Enterprise page) are all related to security, authentication/authorization, auditing, monitoring integration, backup, support, licensing etc.
In other words, the differences are all in areas most likely to be attractive to businesses/enterprises looking to run the MongoDB database as a critical, integrated system in a responsible, supported way.