In a large bowl, dissolve yeast and 1 tablespoon sugar in 1 3/4 cups lukewarm water.
Whisk oil into yeast, then beat in 4 eggs, one at a time, with remaining sugar and salt. Gradually add flour. When dough holds together, it is ready for kneading. (You can also use a mixer with a dough hook for both mixing and kneading.)
Turn dough onto a floured surface and knead until smooth. Clean out bowl and grease it, then return dough to bowl. Cover with plastic wrap, and let rise in a warm place for 1 hour, until almost doubled in size. Dough may also rise in an oven that has been warmed to 150 degrees then turned off. Punch down dough, cover and let rise again in a warm place for another half-hour.
To make a 6-braid challah, either straight or circular, take half the dough and form it into 6 balls. With your hands, roll each ball into a strand about 12 inches long and 1 1/2 inches wide. Place the 6 in a row, parallel to one another. Pinch the tops of the strands together. Move the outside right strand over 2 strands. Then take the second strand from the left and move it to the far right. Take the outside left strand and move it over 2. Move second strand from the right over to the far left. Start over with the outside right strand. Continue this until all strands are braided. For a straight loaf, tuck ends underneath. For a circular loaf, twist into a circle, pinching ends together. Make a second loaf the same way. Place braided loaves on a greased cookie sheet with at least 2 inches in between.
Beat remaining egg and brush it on loaves. Either freeze breads or let rise another hour.
If baking immediately, preheat oven to 375 degrees and brush loaves again. If freezing, remove from freezer 5 hours before baking. Then dip your index finger in the egg wash, then into poppy or sesame seeds and then onto a mound of bread. Continue until bread is decorated with seeds.
Bake in middle of oven for 35 to 40 minutes, or until golden. Cool loaves on a rack.