>> can i do rrf _my_data,1 and expect the whole word to be rotated?

No, it only works with 1 byte at a time. But, the rrf rotates through the CARRY flag, so a second rrf on the next byte will rotate the CARRY right into the next byte.

>> I dont get is how to get the base memory address of the array

At the ASM level, that's what variables are, pointers(address) to the actual memory location in RAM. So low _array gives you the lowbyte of the address of the variable array.
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