5.1.1 to CM12.1 advice please

Hi

Stock 5.1.1 LMY48B
rooted with TWRP installed.

Can I flash to CM12.1 just by flashing the zip from TWRP ?
will I lose any data ? Do I need to worry about bootloader or radio versions ?

If I want to go back is it as simple as flashing my nandroid backup ?

Thanks

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