Hi!

If I choose the first perk in Restoration, does that mean that e.g. I can heal myself twice as much in one sitting?

I have amassed quite a collection of dragonscales. Can I sell them to somebody who can make me an armour or do I have to wait for that perk?

How do I cast heal on NPC?

/J

I believe you need the Heal Other spell for NPCs. Save your dragonscales and/or bones to make the armor yourself. I’m not aware of anyone providing smithing services.

1. well by cutting the magicka cost that might be the effect if you keep using the lower level spells, you might want to try stronger spells instead since they might now be cast-able

2. the final perk for smiting allows you to fashion dragon armor, scale for light, bone for heavy

3. get a spell like healing hands, you cant use cast on self spells on npcs

By "the first perk" do you mean Novice Restoration? It makes spells cost 50% less, meaning you can now cast twice as many Restoration spells with the same magicka pool. Effectively yes, you can heal yourself twice as much, but it will also take longer.
There's another perk called Regeneration. It makes healing spells more effective (150% of the original magnitude). With this perk a single spell will heal more than before.

Vendors don't provide smithing services. The only way to acquire dragonscale armor is to craft it yourself. Technically, you could also loot it, but it's rare, available only on high levels and totally random, so you can't count on that.

1. Yes, for novice level spells only. Combined with the 'Regeneration' perk, you can easily heal a nearly dead warrior-class player to full health on just 100 magicka, and the basic Healing spell.

2. No, you must take the Dragon Smithing perk to smith Dragonscale or Dragonbone armors.

3. Healing Hands, Heal Other, and Grand Healing all heal NPCs. Be careful with Grand Healing though, it can also heal your enemies at the same time.