Do you ask others for their prayers? I'll skip the back and forth and go with it... yes, you do. We all do. Why? Do we need their prayers or shouldn't we just go directly to God as you suggest?
We all want others praying for us. Yes, Protestant theology generally rejects praying to the saints in Heaven for their prayers on our behalf... but then if you embraced Catholic theology, you would be a Catholic.
Most of the dead that you pray to are not in heaven, but burning in Hell.
Praying to them is necromancy pure and simple.
Already addressed.
With a mortal person you can look them in the eye in space and time and relate back and forth on a personal basis as you pray FOR EACH OTHER.
There are many references in the Bible for this.
However, saints in Heaven are not omniscient/omnipresent; those are qualities of divinity. Catholics ascribe these qualities to saints in Heaven, but these attributes belong only to God.