I am a native Bosnian speaker and I teach a Bosnian Online course at Boise State University. I use Bosnian-Croatian-Serbian (BCS) books.

Bosnian and Serbian are very close, with differences mostly down to accent, pronunciation and some vocabulary. Serbian has cyrillic though (although it can be avoided). Croatian, while still very close and easily understood by speakers of either, does have more notable differences. 

As for online resources, Im curious for this myself atm im learning Serbian slowly and want to work more on it now.

Just like Kamenko has just told you, Bosnian and Serbian are almost the same. The differences are very small like: some vocabulary, they prefer to use "ijekavica" and we prefer to use ekavica, dialects, ... 

If you wish, I can teach you Bosanian without any problems. I have tones of materials for Serbian (PDF, pictures, youtube video clips, ...  ) , but whenever I notice some different word, I am going to tell you. 

Have a nice day.

hello! I'm from Bosnia&Herzegovina.. Bosnian, Croatian, Serbian and Montenegrin are all pretty much the same..

I do learn Serbian for quite a while now and  I write and speak in Serbian - ekavica.

Up to now I have not had any problems communicating with people from all parts of former Jugoslavia. There are a few differences in Grammar, pronunciation and vocabulary - but then I do not know all the words in Serbian either.

I do read articles / newspapers etc on the internet and books, listen to the radio and watch films in all mentioned languages.

I also use learning material for all languages because the choice of learning material for just for Serbian is not very big.

I wish you all the best in your endeavour!