What language shall I learn, Treehouse? (use case info inside)

So, I want to see if I can ask an unfair question. I'm getting close to wrapping up the Front End web development track, and before long will be moving into learning about the backend development (lots of CSS to learn, first!). Now, here is where my knowledge is limited..I don't know what I need, per se. So I'll list out the uses that I'll look to be programing into my app:

 Financial

• each module of data will contain a sum of numerical data (i.e. a total derived from values within that module), which then must be compared/referenced to numerical values from other sources (internal, same DB)
• This numerical data (think 100rows x 6 columns) needs to be fed to PDF reporting tools
• Data will be pulled from external (I think?) sources (think a time clock type app on an iPhone) to be tied into each module above
• Comparing this type of data will be a big concern (comparing one array to another, I assume)

Project Mgmt

• Gantt charting abilities
• Assigning physical resources (i.e. people) to time based activities.
• Integration of time based activities with other modules (i.e. a task module will be tied to a time based activity)
• Integration with external data storage (Box, AWS S3)
• Comparing this time data will be a big concern (comparing one array to another, I assume)

Communication

• Every module/widget (don't know better term, sorry!) within the app will need ability to be commented on (UX friendly)
• Integration with SendGrid, pulling numerical data and (maybe) performing math operations on said data (likely handled in app I assume) from DB

Connectivity

• Will tie into several APIs (I assume this doesn't really matter from the language standpoint)
• Will tie into external physical objects to pull data (TBD Arduino devices, Zebra scanners, etc)

Other

• This app will have what I assume to be two UI's: a front end (for the Client to view) and a backend (for the Mgmt team). I do not know if this will be a matter of simply "disabling" certain modules for the Clients view (and having UI the same), or will be two entirely different front end systems just interacting with the same backend data.
• Load times will be a concern I imagine. System we currently use to solve our problem is coded in PHP, and has long load times (probably not PHP fault, just saying).
• There will be a fair amount of images, which I envision being tied to a Modal pop up with add'l information (like a shopping app)
• For now, scalability is not a big factor.

I hope that provides some help on what I'm looking to do with my app. What I am looking for is, given the above info, if there is a language that might be more suitable to learn over another? The primary ones I want to learn being PHP or Python. I am leaning towards Python, as it seems more suitable for mathematical analysis, but then again, I am not performing advanced arithmetics, but rather simple mathematical functions, so I need some advice. I am open to learning whatever language would serve my need best.

I know the best/most likely answer without having too much info is "just learn one and go", but I hope the above might garner some insight on what language might be most suitable for my learning. If not, any advice is appreciated.

Thanks, TH!