datadog,
you are confusing what the Bible actually says about God and what you've been taught God is. This is why your questions don't seem to have a logical answer.
But apply what the Bible REALLY states who or what God is and it becomes a little clearer.
Above all else (meaning that God can be many things), the Bible states that God IS Love. (not a man in heaven sitting on a throne, angry at people, but concerned with chickens.) God IS love, and conversely Love IS God. I do not need to define what love is since I am sure you know exactly what it is. But as you describe it in your mind, know that you are describing God. After all, that is what the Bible says God is.
1) Material wealth is a sign of Jehovah's blessing in our modern day.
If you've become wealthy materially, you can be rest assured that you've been blessed. Who or what has blessed you? Retrace your steps to see how you got to be wealthy, and you'll find your answer.
2) Why Jehovah blesses the growth of chicken populations, but allows active Jehovah's Witnesses to die in field service, or on the way to Conventions, and on the way to celebrate the Memorial?
Here you are implying that 'God' has made a decision, to spare chickens yet kill innocent people. The Bible states that God is perfect and shows no favoritism (to chickens in your example). The Bible also states that 'unforseen occurrences' are a reality. Which is it?
3) Why Jesus is not your mediator?
mediator - a person who attempts to make people involved in a conflict come to an agreement; a go-between. - from wikipedia
The Bible doesn't contradict the definition of a mediator above.
I know these questions might not have been directed at me specifically, but i wanted to get involved in the conversation all the same.