My A77 Kit
Robin, looks like you are off to a good start. A lens like the Sony 400mm "G" would be a big value for birding, but that costs more than most of your other kit put together, so I think you've chosen a good place to start. If you have had luck with your 70-300, that Tamron should give you some similar speed, and the new body has much better high-ISO performance and much better AF, too.
If you want to do some insect photography or other macro work, I'd recommend a macro lens. The Tamron 60mm and 90mm lenses have good reputations (if you search, there have been some recent posts comparing the two). I went with the 60mm because I want it to double as a portrait lens, and I like the focal length and sharpness of that lens (most similar to my Oly 50mm f2), especially for a 24mp sensor. For bugs, you might want the additional magnification of the 90mm or maybe even something even longer.
I am also upgrading from any Oly 620, and hope that you enjoy the A77! How do you find it in terms of handling? Is the viewfinder a night and day difference? I'm probably going for the A65, myself...