if you are using the brewing method, as opposed to the sun or cold water method, you want to steep as you would for a hot cup of tea. whatever you feel is optimal to get the best taste from your tea is how you should proceed. i don't know which teas you will be drinking but too hot water or too long or short a steep will ruin the taste, hot or cold. if you let the tea cool down before icing it pour it off into another pot (for those teas that will get too bitter).
yes, the general rule is double the tea to then add to ice. my suggestion is to measure out the tea, and use the same glass each time, so you will keep the ice amount constant. you can change the tea amount or steeping times to suit your taste.
i once was asked to make some iced tea and did as usual, but didn't give the glass size any thought being so used to my own. the glasses (i pour from pot to glass directly) turned out to be about half the size and the iced tea was too strong until i added water or something.
you can also try putting your tea cup on top of your car while you brush the snow off...instant iced tea, at least where i live.