I do not know what the limitations are exactly, but I think indie can't to post processing effects as there is no render to texture.

the ability to use VS with unity does not depend on the version you use.

you can write DLLs using managed code (c#) any time. if you want to write c/c++ DLLs you need to have the PRO version.

this is not about what A7 can and can't do after you spent months and months extending the original feature-set with DLLs and APIs, etc.
Unity does all of it OUT OF THE BOX without any additional effort on your side.

on the whole learning unityscript or c#...
first of all - let's not call it unityscript but javascript because that what it is: javascript with the unity framework tied in so that all unity commands are available.
most of the older samples in the documentation of unity and some scripts on the wiki are written in javascript... but that is no loss for you, as you can use .js script files alongside .cs (c#) scripts... and even if you do not want to do that, you can easily convert java script to c#, it is just a matter of syntax and typing.