Thank you for the hints. However, I'm still having issue with the bottom part of the puzzle.
V unir sbhaq "lbh unir jba" fcryyrq onpxjneq va gur hccre frpgvba bs gur chmmyr.
Ohg V'z hanoyr gb svaq gur jbeq 12 bs chmmyr 12. V qb unir gur ynfg yrggre Z orpnhfr bs gur obggbz uvag "z15" naq gur svefg yrggre N.
Fb V'z gelvat gb svaq n 'jbeq' fgnegvat jvgu N i raqvat jvgu Z, ohg gur erznvavat yrggref bs gur chmmyr ynpx n Z, znlor vg'f uvqqra ohg V ubarfgyl qba'g xabj jung gb qb urer.
Anyway, it was fun, my SO joined me after I did half of it and we enjoyed it. Thanks again !