I need a phrase for what I approximate by "plan-while-do":
"Do you need anything else?"
"I can't say yet, that will be a plan-while-do project: I get started and come back to you if there are any questions."
My intention is to communicate that I will not take the effort to check for possible questions upfront, as that would be futile.
Depending on how out of control you think the situation will be, you might want to say you're flying by the seat of your pants, shooting from the hip, or that you're playing it by ear. In any case, you'll be making it up as you go along.
Flying by the seat of your pants is mostly American English, and, unsurprisingly, comes from the aviation world. It refers to flying manually, without the aid of instruments or a flight plan. It's commonly used to refer to keeping on track and staying ahead of trouble when high technology has failed you, and you have only yourself to rely upon.
Shooting from the hip is a little different, and generally suggests that you're reacting quickly, without going through all the normal steps and procedures - that is, you've seen your target, and you have to shoot now, you don't have time to raise the rifle to your shoulder and use the sights. It can suggest recklessness as well, shooting without really caring if you hit something besides your target, and not taking the time to do things properly.
I think that playing it by ear is the closest to your request, given the specification that you want to indicate "I will not take the effort to check for possible questions upfront, as that would be futile." It means that you have insufficient information to make a firm plan at this stage, and no way to get that information, so the best option is to have an approximate plan, but to remain flexible.
Making it up as you go along implies that nobody has done what you're doing before, or that you're in a totally unfamiliar situation and no guidance is available.
Plan-as-you-go would be an obvious term for it, borrowing from PAYG or pay-as-you-go.
An example: The Plan-as-You-Go Business Plan on Entrepreneur
More examples available on Google.
