Very good questions!
1) Ultimate skills like Nova scale from your highest offensive stat, be it Magicka or Stamina. It works perfectly fine on Stamplar (even though your CP may not be directly boosting magic damage). Note that Nova is more useful in group play, because its main feat is the synergy. It looks really cool and gives a range dot, though there are arguably better ultimates to use.
2) Templars generally fight melee, because their spammable, Jabs, is also melee. Physical weapons would make your Jabs stronger too, since they give more damage than staves. The Dawn's Wrath skill line has some good ranged spells too. I often played my Templar having one two-handed melee bar, and one ranged staff bar.
Templars are just so versatile!
Just saw your new question. It generally pays off to be either Magicka OR Stamina Templar. If you go magicka, boost your magicka, spell damage, and spell critical as high as possible; for stamina, boost your stamina, weapon damage, and weapon critical. Then you can equip a weapon of your choice, they buff both spell and weapon damage equally - their only difference nowadays is what resource they return with heavy attacks.Thanks for taking the time to answer my previous questions. If you don't mind me asking another, what stat should I put my attribute points into if I wanted to achieve the build you mentioned with the two-handed melee and ranged staff setup?