Wildflower - what I mean by cold foods is actually just that- cold foods- such as ice cream or cold beverages, frozen foods, anything that is very cold. It is hardest on your body to digest anything that is cold, it constricts blood vessels and muscle tissue such as those in your digestive system, which makes the body work harder, and when the body has to work harder on digestion, other things such as detoxification are sacrificed. this is why fasting is so beneficial, it gives your body a break to detoxify itself because so much of the body's energy is expended on digestion alone.
That's not to say that you will get sick if you have a glass of cold apple juice every morning, but in the winter months especially, just take care to keep it in moderation or at a minimum if possible. This is because the natural rhythm and cycle of our bodies is to keep itself warm during fall and winter, and to cool itself down in spring and summer, you go against this and you go against the instinctual workings of your body, you go with it and your body responds better to fighting against viruses and bacteria as it should.
As for astragalus yes, you can make a tea out of the bark, I have a strainer that just sits on top of the cup, which makes it easier to put the strips in without having to break them up. you can decoct four strips in about a pint of water and let it seep for about 30 min. drink about 1/4-1/2 cup at a time, a few times a day if you like, and no, I haven't heard of having too much astragalus, but just as with anything moderation is probably best
The only conraindication for astraglalus is not to use it during times of acute infections or fever because it has a heating nature.
Juliepatchouli- I hope the above comments help, and as for echinacea I too have heard that your body builds an immunity to it- if you take it longer than about a week at a time. But it's not the same way with astragalus as far as I know.