I am wondering if I should go for the bigger shards or not, are the campaign events scripted to go off based on shard count, or based on astral power income rate?

Shard size (count) and finished conversations.

Mostly on shard count, some events are based on fame(plot-unrelated), some are based on Karma, some are tied to specific shards (plot-related sites).
I recommend to choose shards based onavailable techs.
First priority - to build storehouses in provinces, then T2 units and T2 magic schools - that's enough to complete campaign.

thank you
what about anti corruption tech. without it in every province you go bankrupt in bigger shards

Corruption is a multiplier to your expenses.
No expenses (solo warriors, solo mages) - no corruption.
Also, as I explained corruption here
http://www.gog.com/forum/eador_series/corruption_bankrupted_me/post2
Lordcorruption variable can be negative AND games pick minimal - you can have zero corruption if you choose right variants during events.
For example, 2 executed deputies equal to zero corruption from human province.

That doesn't mean it can't bankrupt you. You can't unconquer a province though. And I was talking about large shards. so you conquer your initial 10-15 provinces, then you conquer "lines" to strategic resources as well as having to conquer some of the AI provinces, you end up with a ton of unwanted provinces that are bankrupting you via corruption unless you are playing solo hero

I've had colossal shards fully conquered with the exception of last lord, fully guarded against inquisitors, 8 heroes (6 with army) and corruption wasn't even close to being noticeable.
Your problem, imo, is that you don't conquer enough provinces. More provinces - more sites, more events with gold or possibility to decrease corruption, more slots for economical buildings.
Corruption is capped on doubling your expenses. After reaching breakpoint (all provinces together support doubled expenses) - each new province only adds income. You don't lose anything.

On a side note - you can unconquer a province by making them unhappy (buildings, guards, pillaging) and letting them go.

I wouldn't call it "my problem" since I know to work around it
Always take corruption reducing choices in events
always start out with a solo fighter as my primary hero (adding more later as needed, I was not aware that corruption worked by multiplying expenses, I just figured that keeping my expenses minimal will help my economy)
Avoiding unchecked expansion (I don't need that goblin swamp that produces 0g1c, thank you very much).
I still notice the occasional "income goes down with every province you conquer". Just in my last shard (medium sized) my income dropped from 500 to 400 from conquering a "line" to the enemy capital with my hero. Although that hardly bankrupted me and I won soon after (I also had like 20k in the bank from killing dragons)
Getting all your provinces fully developed requires actually having the tech to do so (problematic in the campaign) and is obscenely time consuming and effort consuming, you got to build a lot of buildings and spend a lot of time exploring. Not to mention you actually need to acquire a whole bunch of tech to actually fully develop those provinces.
I don't think I have reached max corruption before, you just win too fast. And from all the economic buildings, corruption reduction is one of the more profitable ones and when you don't have the time to fully develop a shard and grind it, it is a solid choice of tech to use