Renovating a Duplex Apartment on the 7th Floor - Building Safety Regulator

We've purchased an apartment in an apartment block that isn't a good current state. It is a duplex apartment on the 7th / 8th floor. We need to replace the very rickety spiral staircase that feels like it might fall down but I'd also like to make changes to the layout as it doesn't work in it's current state.

I now know that I need to apply to the BSR rather than building control so I wondered if there were any issues with this plan before I go through the process? All bedroom doors would be FD30 and we would add hard wired smoke detectors in the bedrooms, bottom of the stairs and lounge and a heat detector in the kitchen.

Any advice would be greatly appreciated.