You are most welcome :D
Her heal prioritizes on those who have the lowest hp in your party, and yeap, it re-prioritizes for each of the five heals, once again reiterating how powerful she is of a healer.
And yes, definitely six star her asap, for delaying in doing so was one of the mistakes that I made. The incredible sustainability that she provides makes the game a WHOLE LOT easier.
As for going for attack power weapons, I'm not exactly sure myself. I think this would really depend on personal preference. If you want Night to be able to survive longer so then she can heal your team longer, go for weapons with defense conversions. If you want your heals to become more powerful, go for weapons with attack conversions. I personally use the six star priest wep, which has a def, attack, and function conversion. But I don't use it for the conversions LOL I use it cuz of how badass the weapon looks xD. So basically, go for the conversions for the playstyle that you want: more "survivability" with defense conversions or better heals with attack conversions. The function conversion imo is pretty useless on healers. I think the only useful conversion for function is probably the attack speed one, for it makes your heals come out faster.
As for the skill, I use Energy of the Goddess to generate blocks for my leader, for my team has revolves around either Archon or Mondrian, which are 3-block users. But with a team that is doesn't revolve around 3-blocks, I think there are 3 viable choices:
1) Smile of the Goddess (Mews Skill). This skill is very powerful in general, for it heals your entire team 200% of your Healer's attack power and it grants bonus armor and magic resistance. Greatly increases you sustainability and the bonus armor and magic resistance can help you survive bursts. Thing is though, you have to get Mew first xD
2) Time for Blood Donation! (One of the beginning skills that you have and is further enhanced by Nurspy) Just a great skill overall. Does neutral damage (ignores enemy armor and resistance) and the heal is somewhat decent. It gives you better sustainability and even does some damage :D However, the skill is significantly less powerful than its transcended form... so some work is needed before getting this skill to its maximum potential.
3) Resurrection (The skill that Night unlocks). I think this skill is pretty interesting. It resurrects up to two fallen allies, so basically, all your other team members. If there are no dead allies, it heals for 20% of target's Max HP, so in a way, it is still a pretty powerful heal for tanky characters like Alex or Joan of Arc. However, if Nightingale were to die first, then this skill is completely useless. And the heal it provides is still no match to Mew's Smile of Goddess. This skill has its pros, but it is very situational.
Those are the three skills that I would recommend for you to use, leaning more towards the Smile of Goddess side. The protection skill you are using right now is good at protecting you from bursts, which is very powerful early game. However, that skill is out scaled by the other skills later in the game. But for now its fine, just know that you will have to move on from it later.