It is difficult to pull ahead of other decks in terms of cards in your hand with Oath. This archetype has quite a few viable strategies that each gain an advantage in their own way. The amount of Preordains really impacts how games play out. Fewer Preordains usually requires more Jaces and or Deep Analysis. This is a strategy that can gain card advantage. More Preordains helps to find lands or cards you need.
I've recently been experimenting with cutting tutors and playing three to four Pyroblasts, three Flusterstorms, and Four Missteps. I've put up two 5-0's in the last few days with this strategy, so maybe there is something there. I've been winning matches that usually gave me the most trouble such as BUG Fish and RWU Xerox. The somewhat difficult match is still the Tendrils version of Paradoxical Outcome. I have found that I basically cannot tap out. Every time, without fail, they will combo out if I tap out.
I am a big proponent of Mission Briefing in Oath. Recasting Time Walk or Ancestral Recall can give the deck an edge when it needs it. I almost consider this card as important to the deck as Gush.
As far as Gisella goes, it is great against creatures, but so is Inferno Titan and other Oath targets. I include it in the main deck because I want as good as chance as possible to beat Dredge.
Matt explained when to cut Oath of Druids pretty well below. The other aspect to cutting Oaths is the mirror match. I have found over the years that the best strategy in the mirror is to cut all of the Oaths and side in one to two Nature's Claims and one or two Sudden Shocks. The mirror becomes a game of who can gain an advantage from any Oath on the board by having more Orchards or using Sudden Shock to kill the Spirit tokens under your control. It is also a race to hard cast your creatures. You can still keep some number of Oath's in after game one, but this strategy runs the risk of your opponent using it to win.