I see no issues with playing it that way.  Well done.

Update: I have played a few more times and have been beat hard. The whole deck concept is based solely on a mechanic that is difficult to get out but once the engine rolls then it works very well. A few inconvenient flips of the encounter deck or not having the Galadhrim's Greeting show up within the first few rounds means certain destruction. THAT TROLL WILL WHOMP YOU HARD WITH NO BEORN (PERIOD). So ... fear not.

Also as far as the deck construction goes the rules for deck construction are at the end of the rule book, which at no time limit your using of out of sphere cards. but it does give you a warning,

"A player should also make sure that all
the cards in his deck belong to a sphere that matches
at least one of his heroes’ resource icons, lest he find
himself with a dead card he cannot hope to play."

I can hope to play those cards...

As for the deck make up I used all the spirit cards I had and just threw in Gleowine x 2 and Beorn x1. That's it. Like I said a non 50 card deck but a good example of a 50 card make has been listed by CAlexander

Thanks CAlexander for the 50 card make-up I'll be sure when I get enough cards to play around with it further.

 Iron-on Ghost, you are a genius and your combo is 100% legal. SaF specifically states you can pull allies from any sphere. I would't find it highly unlikely that FFG would errata such a combo away; combos like that are supposed to be what CCGs are all about. If deck building choices were obvious, the game would suck. Like CAlexander, I wonder if this is perhaps Sky's first deck-building game. 

You do not need this combo to beat scenario 2.

I've been playing 3 games and won all of them using only spirit deck with 3 gandalfs. It is easy, you quest with Eowyn, counter all possible cards that can screw you (and some of them do nothing if your threat is low), keep threat down, around 20 and destroy all enemies with the sharpshooting hero knight. Important: do not touch the troll. You can play stage 1 for hours and nothing can hurt you, reshuffling your deck all the time, putting threat level to 0 value, prepare the board with your every ally and finally screw the troll with 3 gandalfs strikes (when you deal last hit you should have 2 gandalfs in hand). Then you procede to quest with the army of allies and in the same turn you finish 2nd part of the quest and go to stage 3, which you win in 1-2 turns. It is possible to do that with 0 threat and after playing stage 1 for 3 hours (if you have time and patience) you will have tons of victory points.

I know 3 out of 3 is not a big deal, but I'll play some more games and check if spirit wins all the time. The important thing is to not let troll engage you, so you can't finish stage 1 of the quest and during this stage you can go through the deck multiple times.