I've considered several things, either losing water for air, getting rid of the Forest Sprites for Firefly Queens and maybe some copies of Sanctuary for more regen goodness, Shockwaves for more effective CC and bless for keepign stuff alive;
This is possible. Bless doesn't sound too useful.
Swapping out water for darkness to get nightfall for buffed skeletons and to give me access to Steal for some acutal PC(!)
I'm more skeptical of this.
dropping water completely and going down the route of forest scorpions and lots of poison
And this.
Allow me to elaborate.
Decks can range from 30 to 60 cards. A 30 card deck will last 24 turns (you start with a hand of seven) or 23 if you play second (the first player does not draw on the first turn), when you draw one card per turn. Most games you play in Elements do not last this long and most exceptions fall into the ai5 and ai6(false god) categories. A typical game is probably 10-15 turns (i have no statsitics on this) and a fast game can be over in 6 turns or even faster.
A smaller deck has two advantages. It allows you to take only the better cards, increasing the average value of a card you draw. And it provides you with more consistent draws.
A larger deck would typically be played either to add the option of decking out your opponent, or when you have draw power (usually in the form of hourglasses although golden nymphs would apply as well and possibly sundials to a lesser extent; precognitions are most often used in 30 card decks to make them "appear" even smaller). A slightly larger deck also might be used to hone in on the proper ratio of cards in your deck.
You're trying to make a deck for AI3 and T50. As unit748596 and Higurashi mentioned, large decks are not the standard. There are at least two reasons for this. The composition of the decks in AI3 and T50 make blitzing a sensible strategy. The decks in AI3 are generally large cumbersome and slow. The decks in T50 are oftentimes farms, in which case a win is not in doubt and you may as well win as quickly as possible. The second reason is speed. More games means more wins. A slower deck is unlikely to achieve more than a slightly better win percentage (not enough to compensate for the sluggishness).
I still see value in playing a large deck in AI3 for a couple of reasons. It gives you experience with more cards and card combinations. In a small blitz deck you may have as few as two different card types (excepting pillars). With a larger deck you familiarize yourself with a wider range of cards and how they interact. This is of limited utility as time goes on and you become accustomed to each card. Additonally, it may help you develop ideas for pvp decks. Pvp decks are often bigger than AI3/T50 farming decks. Small blitz decks will likely always be a staple in the pvp metagame (if they aren't then something is out of balance), but stalls will have their say as well. A 60 card deck without draw power is uncommon even in pvp, but among stalls there is a tendency towards getting bigger to deal with other stalls as stalls become more prevalent, so i wouldn't discount the notion altogether.
Hopefully this sheds some light on my suggestions above. If you are running a large deck, defense is king, so buffing skeletons or dealing poison damage shouldn't be a priority (these strategies would be more effective in a smaller deck). But keeping your side full of fireflies so that you can heal 100 damage per turn could be effective against some decks. (You might want to mix in a jade or reflective shield so you don't get bolted to death though). Bless is more often used to boost creatures' attack values (particularly creatures that copy themselves or dive). Guardian angel is a more likely source for healing, although in this deck i don't see creature-healing as a high priority.
If you have your heart set on playing a large deck, i could recommend trying earth/light or earth/light/water. The stoneskin/miracle (once you have some miracle cards) synergy is useful.
Finally keep in mind that, as with most anything, learning is gradual. Don't be afraid to experiment with different ideas. Even if it slows you down at first you will learn from your mistakes (if you made any) and have a better understanding of the game in the long run.
Cheers and best wishes for continuing good fortune
--Chroma
