Will they be expecting kids to buy instruments or provide their own?
If they don't have existing strings, and the kids don't have instruments, then this program is DOA.
You can't teach beginner strings and then have them move into mariachi style performance in a semester. That's like asking your first-year-in-country ELLs to be in a literary criticism class discussing Shakespeare. You need to explain the scope and sequence of band instruction and the progression of band and orchestra curriculum. Teach your admin.
Your principal also needs to be informed of the cost of the equipment. It's also not a one-time cost, either - you'll need to continue buying violins, vihuelas, guitarrons, and the like as the program grows. This will negatively impact the band program without a budget increase.
If they're saying "teach the class" without providing funding and structure for it, ask the admin how they plan on solving those problems, since this is NOT your purview.