Towards making a perfect yellow cake

I made the basic yellow cake quite a few different times with different recipes and I don't have a favorite one yet. I always forgot to take notes. So here I am starting again. This time was not too bad but I made some mistakes which I only realized after the cake is done :D

So here is the recipe I used:

Ingredients:

Land O lakes spreadable butter-1/2 cup (Prefer non-spreadable and unsalted butter)
Powdered sugar-1 1/2 cups (DON'T USE POWDERED SUGAR. See mistake 2)
Eggs-3 medium
Bread flour-2 cups (Preferably use 2 1/4 cups of all purpose flour)
Salt-1 tsp
Baking powder-3 1/2 tsp
Whole milk-1 1/4 cups
Vanilla extract-1 tsp

Method:

1. Pre-heat oven to 350F.
2. Grease two 8 inch pans or one 9X13 pan (I think 9X13 will be too big. If you want a thick cake and use 9X13 pan, multiply the recipe by 1.5 times) with oil/butter and add 1 tsp of flour. Tap the pan so that flour spreads evenly and dust off the remaining flour. If you have parchment paper handy, line the bottom of the pan with it. In this case, dont add any flour. just greasing with oil is enough.
3. Add softened butter to a deep bowl and add powdered sugar to it.
Mistake 1: I was supposed to beat them both and make it fluffy but when I started beating with an electric mixer, powdered sugar was all up in the air and on myself. So decided to proceed to next step without making it fluffy.
4. Add eggs to the above mix and beat well at a low speed.
5. Now continuously add flour to the above mix and keep mixing with the mixer at low speed. Add salt and baking powder and mix well.
Again, the flour was all up in the air. So I decided to add entire flour at once and mixed by spoon. The end product was a thick batter.
6. Add milk and vanilla extract. Now beat with electric mixer at low speed until everything is properly mixed. Then beat at high speed for 3 min.
7. Distribute to the pan (s) and tap to spread the batter evenly.
8. Bake for 30-35 min. Turn off the oven when a fork comes out clean from the center. Remove and let it cool for 15 min.
9. Then turn the pan up-side down and tap to release the cake. Cool on a cooling rack or a plate lined with paper towel for 15-20 min.
10. Proceed to icing or make tres-leches cake or eat with ice cream.

Mistake 2: To my surprise, cake was not sweet enough. I then realized that powdered sugar tastes less sweet than granulated sugar. So never use powdered sugar.

Mistake 3?: You are not supposed to use bread flour for cakes. I didn't have all purpose flour so I used bread flour. May be the texture is little coarse because of this. Not sure.

Mistake 4?: Use non-spreadable unsalted butter for best results. The cake turned out alright but may be it will be more better with non-spreadable butter. 

Conclusion: Next try, use regular sugar, all purpose flour and non-spreadable butter.