For a birthday cake; Flour sift vs. not sifting? Egg white vs. whole egg?

About sifting:  don't bother.  It may add a little lightness to the cake batter hence the cake but it's been a long time now that the production of flour has left in the kind of particles that used to necessitate sifting.  Probably more important than sifting the flour is weighing it, but then you'd have to find a cookbook with a recipe you like that has measurements in pounds or grams.  I don't have one.  I recommend trying to find my favorite yellow cake recipe.  It's in Kathleen's Bake Shop Cookbook.  Here are the ingredients:  2.5 cups APF, .5 tsp baking soda, 1 tsp baking powder, 1 tsp salt, 1 cup butter, 2 cups gran. sugar, 5 eggs (separated), 1 tsp vanilla extract, 1 cup sour cream.  Icing is dealer's choice.  Directions are the pretty much the same for all basic layer cake recipes.

Eggs:  whole eggs will give you not only a slightly yellowish color, but will make a different cake altogether.  Do you want a denser, richer mouth feel or a light and fluffy feel.  The latter is egg whites only and gets you an angel food cake.  It's got a slightly different technique from the whole egg-type cake.  The former is my particular preference.  Read about the differences before you start out.  It won't take you long. 

I have been baking alot of cakes and pastry lately. I would definitely recommend sifting. I use KAF professional flours and there is not a big problem with them getting hard clumps. Other flours may clump depending on the time of year and brands. Sifting does more than eliminate clumps. It helps distribute other ingredients more evenly throughout the flour (salt, soda, b-powder, spices). Since the flour portion really shouldn't be mixed into the batter it should be folded, the better the dry stuff is distributed before incorporating makes a difference. Also the lighter and fluffier the flour the more easy it is to fold in and coat the flour with the fats. Also keep in mind the fats should be room temp. So, take the butter and eggs out of the fridge and let them sit on your counter for a half hour or so. You can also warm the eggs by placing them in luke-warm water for ten min or so. First the butter must be creamed properly. Mix the butter by its self to the consistancy of mayo. Then add the sugar and mix (cream). To many people dont let it cream long enough. You are whipping air into it. That takes about 3-5 min in a KA mixer on med with a beater. Time depends on the temp of the butter. It should lighten in color and be fluffy. Rub some between two fingers, it shouldnt feel gritty. Then add the eggs. This is an important step. Eggs are one of the leaveners in the cake. Air trapped in eggs expands, then when the eggs cooks it traps the air. Mix the eggs intill the mix comes together lightens in color and looks fluffy/pillowly (if thats a word) usually about 2-3 min. If you start to hear a slapping sound its done. Now fold in the dry stuff so you dont destroy all the air bubbles that you made with the butter and eggs. This will produce a nice light cake with wonderful texture. You will never want to buy another store cake of box mix again. One more thing. Use whole eggs, dont try substituting. The fats are there for a reason. If you want a lighter cake try one of the sponges like angel food that use whipped egg whites. In those cakes sifting and folding is even more important.