check this out as well it gives you an idea of what perks in smithing do with improvements.
http://www.uesp.net/wiki/Skyrim:Smithing#Item_Quality
its all how you want to rp but in my opinion its more fun for extra sneak perks or alchemy, illusion, archery. smithing 100 gives you flawless on the gear with just steal and improve enchant. But if you want to make your own, it really is a waste of time imho.
So i could improve the Nightingale armor with smithing i've not used Smithing yet believe it or not.
to improve that you just need steel -> improve enchanted and that will get you flawless, in my opinion going up to legendary to spend all those perks are a waste since its above the armor cap. Besides you need a special blacksmith potion.
What I would do is decide, do you want to make dragonscale or use nightingale?
Then decide what weapons you want; what i use is dual dagger with mehrunes and valdr's lucky dagger.