The NEC does not address smoke detectors other than through regulations of wiring that may power those devices.
Your local building and/or housing regulations will address your question. Requirements vary widely.
Some are nonsensical. The State of NC permits detectors to be on the ceiling or wall near the ceiling. But some cities in NC require them to be on the ceiling only.

Get a compentent Fire / security company involved.

If it was me I'd think about a system where the detectors communicate with one another. If one goes off, they all go off.

I'm less concerned about 'code' and more curious about best practice for safety. I agree a system that is wired together would be ideal, but I'm not certain I'm in a position to afford such an outfit. I may have to base my design off of the vendors recommends it sounds like. Thanks for the feedback guys.

JMHO, but I put smoke detectors:
- at/near the top of stairways, and anywhere smoke might 'pool'
- in any room with a water heater and/or furnace
- in the garage and laundry
- in the attic, or anywhere a fire might go unnoticed until it's gotten a good start

Placement would be on the ceiling, at least 18" from any wall, or on the wall about 18" from the ceiling (air currents from any source are more apt to dilute the smoke concentration close to the wall/ceiling junction)
Placement would also be where it's not a major effort to change the batteries at least annually.

CO detectors - at least 1 per floor, plugged into a wall outlet that is not cut off from normal room air currents.

JM$.02W

Call your local fire department. They will be happy to come look at your property and tell you both what your local code requires and also what is recommended beyond code.

You can get WiFi Smoke and CO detectors like Nest for example. They still need power but the interconnect is achieved through your network. You can also get notifications of alarm events on your smart phone, and control the system via PC or smart phone interface.