My plan usually starts to grow while I am piecing the top. Although I have been known to want to do a feather design and deliberately made the top to show it off. I have also finished the top with no ideas, which is dangerous as I begin my next top and don't finish that one.
so it depends.

As I used robotics in quilting I usually have a plan all laid out. I use a program called ProQ Designer where I can put quilting patterns on the screen to fit the quilt I'm working on, arranging them, tweaking size, etc. till I have what I think will be a good layout. I can also add the photo of the quilt behind it so I can see how it will look on the quilt before I do all the work. I mostly custom quilt as I find that easier for me than E2E but that's just me. I also keep in mind where all the seams are on the quilt so that will help with the planning of what pattern I'll use.

I have several 'go-to' quilting end to end patterns that I use for most of the charity quilts I make. One is circles and stars, another is a swirly design. Both look good on most quilts because they're sort of neutral with regard to the quilt colors, theme, etc. The swirly design goes FAST and looks great as well, so I'm using it more often.

For quilts that are going to a special person in my life, I might use either of those as well, or pick an end to end that is more customized to the person and the quilt.

I always make the choice when I'm ready to quilt the quilt.

I don't start thinking about the quilting part until the top is finished and I'm pin basting. I quilt on a DSM with free motion or a walking foot. I don't do anything fancy, just stipple, SID, or cross hatching. The simplier the quilting the better.

Me, Myself and I have regular discussions throughout the process; sometimes it can get a little heated, but we work it out and compromise so we're all happy... Yeah, the Furbabies look at us that way too....

I usually have three projects going. One that is being quilting, one that is needing binding, and one that I am gathering patterns (usually have to adjust them in some way so that they end up not like the quilt pattern I start with), getting the fabrics (after 4 years going on 5 years of quilting) from my stash, if I need one or two fabrics to complete it, I go to the local quilt store or JoAnn's, Hobby Lobby or online to get a missing fabric that I think will work. Fix the pattern and add my own tweek to it, then start cutting, quilt a while and then work on the binding. I like to do the hand-quilting and hand binding in the evening while we are watching TV.

I sometimes draw out the pattern on graph paper in ink. Then I will doodle with a pencil until I get the look I want. It also helps me find out how to move from one block to another while I FMQ. I use the pencil so that if I don't like something or it doesn't work I can erase and try again. I also put too much time into thinking and then never get anything done.

I usually have a pattern in mind and a general ideas of the colors I want but that's subject to change with when what I see in my head doesn't line up with what's available in reality. Or I find something I hadn't considered and it's "just perfect" for my project. That's one reason my stash keeps growing! LOL

Who knows??? Even when I think I have a design POOF and there is a new design piece. Right now I' m working on a green and purple(???) quilt. I am not a purple fan but I saw a purple and green quilt that I loved BUT could not part with the $250. Two years ago I got 2 packages of green and purple fat quarters as a Christmas present. I bought additional purple but could not find a pattern. I bought a pattern and am in the process of adapting it for green and purple. Of course there are 3 other quilts I am working on at the same time. I have a problem as I will begin to work out a quilt design as the idea hits. Very seldom do I plan out an entire quilt before I begin. I have a plan in my head as I put it together but am always open to new ideas:D

I ponder quilting designs as I go along. They change frequently! When the top is done is the best time for me to work out the details. :)