There are multiple questions in your query, making it harder to reply fully, though I try to put you in a picture:
Talend Open Studio runs on a GPL v2 license, as stated in this discussion it shouldn't be a problem to run with this one an in-house solution. You can also read a GPL v2 content (specifically point 2) which allows such solutions to run free of charge.
Comparing Enterprise and open source version, there is a question on SO from which you can partly digest what may be short comings (like missing SVN and job scheduler in open source version) between the two. As always you can overcome this limitations (job scheduler can become windows scheduled task or cron job in linux, versioning can be done externally). This clearly shows one backdraw: you will be spending more time scripting around processes you create with open source studio compared with the enterprise version so you would need skilled persons for that (which is nowadays most expensive source).
Indeed the Talend Data Fabric is now the product name of an enterprise version of a Talend Open Studio, though it looks like there are other products/components which you can purchase for enterprise. Sorry I cannot be more precise on this field as I am not using enterprise version, but you should get this information via contacting sales department or asking directly in their support forum.
Hopefully I made this a bit clearer.
