20d, I think ‘ya done good.
What is the intended use of your photos? Glossy magazines or sold to stock agencies? Printed for at home display or just sent to family members via email?
If the latter, then differences of 2.8 prime gives you will not matter all that much, while saddling you with 200mm which would wind up what seems like limited usage. At least the 2.8 zoom gives you multiple low-light and image stabilized focal lengths for the outlay.
The 300 f4 has gotten great reviews.
I see you went with the 2x Extender. I would have gotten 2 and 1.4 to see which one does it for you and return the one that does not.

