For example, lets say a group of people are learning Baba Basra. If they have a question on Tosafos, would it be appropriate to ask here? I assume its not a general enough question to be worth posting to such a broad audience. Maybe there should be branches of this site for more specialized areas?
Yes, you should ask the questions here!
StackExchange sites are supposed to cater to "long tail" questions - questions that are too narrow to have been written up on any other online reference site.
There are branches of this site for specialized areas. They're called tags. Tag your question to set it in the right context, and people who are interested in that context will notice it, and some will hopefully be able to answer it. For your example, I'd recommend the talmud-gemara, bava-basra (not existant yet), and lomdus tags, to begin with.
To add to (not disagree with) @IsaacMoses's question, one of the criteria I use for determining a question's appropriateness for the site is passing the following test: If I were to ask this question to 1) the people I encounter on a daily basis or 2) Google would I get a satisfactory answer? If the answer to both parts is 'no' the question passes!
According to this criterion, a question like "why does Tosafos in Baba Basra say 'yibum vachalitza' if it really only means 'chalitza'?" would work, but one more like "which page in Baba Basra contains Tosafos 'hechi dami'?" would not.