Just off the top of my head, I would say no, do not delete the text in the lyric window.

Why not create a small test project and try it out? Then you will see whether deleting the window text causes you to lose the lyrics in your composition.

… When I finish one voice, can I delete the text and place the text for the altos in there? That way I can keep an overview of the whole lyrics for one voice …

Why not use multiple “lyric containers”?

In the Lyrics window you can switch between different lyric containers:

Verse 1

Verse 2

Verse 3

&c.

- you can also use Sections:

Section 1

Section 2

Section 3

&c.

- or Choruses:

Chorus 1

Chorus 2

Chorus 3

&c.

Finale-technically speaking there is no difference between Verses, Sections and Choruses.

They are just there to help you organize the lyrics.

A definite NO! Deleting the lyrics from the lyric window will erase them from the score. Use Peter's suggestion: Sopranos in Verse 1, Altos in 2, etc. You will have to adjust the baselines, but only once.