Big question I can't find on Google; will it combine Blackshark, FC3, and A10C in one install?
If you install the separate modules (A-10C, BS, FC3 and P-51) into DCS World you can consider this one install.
But you have to buy the modules separately and then install them into the free DCS World environment.
If you have previous standalone versions of A-10C, BS and or FC, you can use those serial keys to activate the modules. No need to buy them again.
For FC3 to install into DCS World, you need to have one of the original LockOn (or LOMAC) versions and install this as a stand alone prior to install FC3. This due to UbiSoft being the legal owner of these titles.