Well, first of all, I just want to say welcome to the forums, and that this isn't bad for a first hero suggestion.
That being said, let's get into it, shall we?
First of all, Let's take a look a hero already in the game, Brother Victor.
- 1. Fist of the Heavens - Target Unit
Heals for X hp on the target ally or deals X magickal damage on the target enemy.
All conditions that Victor has will be transferred to the target enemy.
2. Martyr - AoE Indicator
Heal allies X life if they have a condition and transfers all of their conditions to Victor.
3. Valor and Zeal - Passive, Channeled, No Target
Victor has X bonus life regeneration. While channeled, he losts his bonus life regen but nearby allies gain a Y bonus to life regeneration.
4. Absolution Aura - Passive, Aura
Units without conditions within range of Victor will take X% less damage from all sources.
In terms of role and function, these heroes are fairly similar. William has a skill that removes all conditions in an AoE (which is a step up from Victors, in which he just takes the conditions on himself) and increases their attack and movespeeds. Again we have overlap between Valor and Zeal and The Banner of Hope, which are both AoE regen, the only difference being that Victor's is channeled, while this is a ward that additionally can block conditions. Hero Attack is unique to William, but you've got to think to yourself for a second as to if the skill really fits with the rest of the hero. You've got three AoE buffs, essentially, and one attack that doesn't take advantage of any of those buffs. In all honesty, it's difficult to come up with such a skill, but if you could , it would significantly strengthen the quality of this hero (I'll go into a bit more on this later). The Ultimate skill is a significant weakness in this hero, not because it wouldn't wtfpwn, but because of two problems. First of all, it's just doing way way way too much. You can't honestly expect this skill to heal all allies, damage all enemies and buff every aspect of all allies within an AoE, that's too much for one skill to bother with, and it'd either have to be tweaked so low that it's almost just a drop in the bucket, or so high that it's obnoxious. The other problem is that it almost 100% overlaps with the first skill, which is a very bad thing. You want all the skills to compliment one another, and you definitely don't want one skill making another nigh worthless...
As to how this hero can improve... Well, there's not too much I can say here, honestly. The role is too similar to Victor's for the hero to ever really come into it's own without a massive overhaul. But since that's almost out of the question, let's look at doing what we can here, eh? The ultimate and the third skill are the real problems here, so far as I can tell, so let's think on those...
Hero Attack needs to take into account allied buffs as well as be a direct (ish) damage attack. Hows about the following...
Ultimate:Hero Blade- Channeled Line Attack.
William raises his blade above his head, charging it with power. For every second spent channeling, the damage of the attack increases by X, and the range by Y, for a maximum length of time equal to the number of unconditioned, buffed allies within Z AoE when the spell begins (likely times some unit of time, maybe 1/2 second per ally).
Significantly different, and in the place of the ultimate, but essentially the spell takes advantage of the buffed allies for a giant, heavy attack, but only if you've got enough allies to power it.
Now, as for the new 3rd skill, really it's up to you. I'd recommend some interesting and useful passive, plausibly something like this:
Return to Sender- Passive Aura
Whenever an ally is given a condition within X AoE, that condition is instead applied on the enemy that gave them that condition, and the allied unit steals Y health from said unit. Triggers at most once every Z seconds.
Not perfect, but it could work... I dunno.
Either way, good first hero, I hope to see more.