To answer an uncertainty of yours Ellisior, assaults do not matter for Nyzul, but you do gain rank up credit for Nyzul wins.
Leading a group is easy as hell now a days, 3 people is ideal IMO with either 2 rapid solo DD (I.E. drg/mage, blu/--- being my personal favourite) and 1 healer, or for general climb floors any 3 soloist DD but with 1 person /whm for certain -na spells (blu or drg /whm work exceptionally here again).
You gain 5 points for your first succesful Nyzul, and 1 point per winning run after that, I got to SL from nyzul only back in the day.
Also dont waste your time bringing in crap like Drg/Blu. One healer and any 2 non fell cleaved DD's will clear faster then solo jobs. Ive been doing clears for a friend's tokens for yagrush and we always get 10 floors, highest was 16 using Whm + 2 Strong DD. 16 floors was recent with 5/5 Shoha sam and relic gun. We usually went 2 ninja's 1 kannagi and would never get less then 10 floors.