These are some rather open ended questions, but this should at least get you started:
Developing SQL Server is normally a more general term than programming with T-SQL. In other words, you may write T-SQL procedures or scripts, write C# programs that use SQL Server, use SSIS, or even use a non-Microsoft language like Python to write a program that works with SQL Server and call it developing for SQL Server. In contrast, programming with T-SQL refers specifically to writing scripts, functions, or procedures using T-SQL by itself (or at least as the primary tool).
The key to being successful with SSRS is really to work closely with your users. I think this is true of any development project really, but more so with SSRS since you generally have a very small number of users with very specific requirements. As far as learning the technology, look at the training material for MCTS: Microsoft SQL Server 2005 Business Intelligence. It covers SSRS quite well along with SSIS and SSAS which are useful things to know if you want to work with SSRS. You may or may not find the exam itself worth taking, but the study materials will give you a structured approach to learning.
Just like any career change, I would suggest studying the technology, practicing with it, and trying to find other people that use it (PASS group in your area perhaps?). Then start applying for jobs.
SSRS is a good field to move into, but can I ask why you focus on that one? Especially if you are just getting started, you may want to look at starting as a general SQL Server Developer and then specializing after you have more experience.
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