Question with the DMA

Usualy no. Normaly you need to erase an entire page before you can write to flash memory.

But if you want to write only once (and sequentialy), yes, it should be possible.

Actually that is unlikely, after each write you probably need to poll a status register until the write itself has completed.

Clearly it is possible to design a flash interface that performs this status test (or even a dma controller that will do status reads and compares and loops), but it is unlikely to be done!