Multiplication of bacillus subtilis
I am basing my answer on this document issued by one of the departments of the Ludwig Maximilian University of Munich.

Bacillus subtilis:


Doubling time: 30 minutes
Incubation temperature: 37°C
Growth conditions: strictly aerobe


Recommended media:


Luria-Bertani (LB) broth/plates - (for everyday use)
Difco Sporulation    Medium (DSM) - (for long-term storage)


You can find the formulations for the aforementioned media by following the link above.

With regards to the latter part of your question, the easiest way to tell (and doesn't require any "high-tech" lab equipment) whether your cells are multiplying or not is to inoculate a broth and see whether there is turbidity after a certain time of incubation. However, please be aware that you may have cross-contaminated your broth so unless you do further testing you cannot know for certain if it is Bacillus subtilis in your broth.