Balayage ombre for the summer

Oops my initialy pic was too large so here is my hair now.

Since you have already processed your hair twice, it is best if you wait at least one month before applying any more bleach or peroxide products.
I would start by removing the demi color using a color remover and working from there. Since your hair is already bleached,20 vol is more than enough. And you should do bleach baths, not full bleach.
I have almost black hair, and one bleach session with 20 vol gets me to  Pale yellow. Yours definitely doesnt need more than 20.

Thank you puerkz! I definitely plan on waiting a while before starting "phase 2" of my hair lightening.

For the demi, the color I actually ended up using was too light and didn't do anything whatsoever to make my hair less ashy (I had gotten an ashy blonde because the hair sample looked like it was the same level - maybe 1 lighter - than my current hair but in ashy tones). Should I still remove it? I assume although it doesn't show up, the dye is still in my hair right?

When you suggest a bleach bath, you mean diluting the bleach and applying it all over right? I don't want an all over colour, so do you have any tips for that? I had previously applied the bleach using a balayage technique so that there are no harsh lines and it worked for me so I was thinking of doing more of the same?

Yes, a bleach bath is just bleach mixed with shampoo.
My sister had several sessions of balayage done to make a soft ombre effect and it seemed to work well . So if you are happy with that technique then it is probably best to stick with it.
I would still use a color remover just to remove any possible dye as the bleach will remove that first before lightening your own color. So it will work best if you remove any dye molecules in the hair.