Quick Healer is then a reasonable quality, but not better than Mentor Spirit. I would still take Mentor Spirit. I don't think there's anything you can reasonably drop to jam in Quick Healer.
Sound Cloud is far better. The reason is that the cloud spells do Suppressive Fire which is going to do Force DV. If you cast at, say, Force 5, then Blast Cloud will do 5 DV, resisted by body+ 1/2 impact. That's probably going to do like 2 stun. Whee. Sound Cloud will do 5 DV resisted by only Body... and anyone who takes more boxes than their Willpower is nauseated. Doing small amounts of Sonic damage is useful; doing small amounts of Blast damage, not so much.
HC can be read in two different ways on two different aspects:
1. Do you combine penalties for sustaining spells into one big penalty? Is 2 spells one -4 penalty, or two -2 penalties?
2. Do you take one complex action, set your HC to a single thing (like "Sustaining Penalties"), and then roll out? Or do you have to take one complex action, then immediately perform the task, then you have to take a new complex action for each new task? So, like "no sustaining penalties on this next spell I cast" "cast spell" "no sustaining penalties on this shot I am about to take" "take shot."
2 determines whether the power is total crap or not. If it's the former interpretation, 1 determines whether it is good or awesome. The idea is of course that you use it to keep a bunch of spells sustained, or at least 1 in any case. It's better than a sustaining focus because the max force is uncapped.
Re: Firebringer, I think Firebringer should be a dvergar; probably Brokkr. Brokkr is associated with crafting (he and his brother Eitri, who should probably be Artificer, made a bunch of the famous things the gods uses, like Gungnir and Mjollnir). Brokkr is the one who works the bellows, whereas Eitri does the crafting (so it makes sense that Brokkr is Firebringer, and Eitri is Artificer). He nearly gets in trouble by betting against Loki which fits the "plans don't always work out" aspect of Firebringer. It's not perfect, because I don't think the dwarves were much for actually sharing their knowledge, but it's decent and certainly better than Loki or Odin.