Will there be a mix of windows (mullion and non-mullion) visible from the front of the house? Or only in the back?

no change to the front, the mix would only be visible from the back.

Not a design expert- just someone who remodeled their own home. We have some windows with mullions on the front of the house (they were that way when we bought the house), but none of our new windows use that style and it's not a problem. We also have a mixture of plate, casement and sliders.

They are unified because all are white vinyl, all have the same exterior trim around them. The ones with the mullions are on a separate face of the house, so you never seen them side by side with the non-mullioned windows. As for the differing styles, it is functional and therefore doesn't stand out to the eye (i.e. the casements are part of big plate window combos while all the standard sized windows are similar sliders).

So while technically they don't all match, the brain doesn't really register it as mismatched.

I think it is fine to do this in the back of your house. It will not ruin the look. And, they look like very pretty windows.

It will bother some people but not others. My last house had mainly double hung windows but, as was often done in the 80's, also had some casement windows. They were all Anderson and all of the double hung had grids while the casement did not. I was able to order grids for the casement windows directly from Anderson, even though the windows were almost 40 years old. It helped create a more uniform look without changing the actual window style. Prior to the reno we lived with the mix of some windows having grids and others not for about a year and it did bother me the entire time.

Can you get the removable grids? I hated the grids on our house and was pleasantly surprised when I realized I could easily pop them off :) If whoever buys the house in the future wants the grids it will be easy for them to reinstall.

Just buy the fake snap in muntins for all the windows.

What if you add a transom with the grids? I personally like the grids but wanted a less obstructed view above the sink so we combined the two ideas. The rest of my windows have grids so it correlates.

I dislike grids but the advice to get windows with removeable ones seems to be agood idea. I agree if this is only on the back of the house probably not a big deal.

I agree that it's fine if it's only the back of your home. I also like the idea of removable ones that's a good suggestion. I think it's more of a personal preference if you won't be bothered by the look you should do it.

No muntins. this will cheapen the look of your home

Keep the window style consistent, final answer.

Stick with consistancy.

I have seen the term grids used by window companies themselves - just because there is a technical name for them it doesn't mean there aren't other laymans terms that aren't valid to use as well. Case in point, Pella Windows themselves refer to them as grids in this article. https://www.pellabranch.com/windows-doors/windows/window-grid-styles/ 

People call soffits fur downs as well. No reason to not learn and use the correct term. Even if a manufacturer feels the need to dumb it down.

Ok everyone, I'll update the post to use the correct terminology.

I would not even trust Pella's use of words as terminology.