How can I save multiple selections only (made w polygonal lasso) w/o losing the subsequent steps ?

Get the number of active selections

When selections are saved, they are stored in the Channels panel.

You will have more flexibility if you put each filled selected on a separate layer. Layers can be merged at any time.

You can lock transparent areas to make it easier to fill a layer with a different color.

Are the areas in their own layers or at least all in one layer that is not the image layer? The paint bucket is an old, worthless tool. I'm guessing you are fairly new to PS - just because you used the paint bucket. A better way to do this is using layer masks. You mask out the areas you don't want to change, leaving the areas you want to change and then you can use a color overlay or lots of other adjustments / adjustment layers. This also saves your selections. I have an old video that introduces masking:

I don't know about your experience level, so I'll try to keep it simple. Put the selections and fill them all on separate layers. Lock the transparency on the fill layers, then you can change the color very easily without saving the selections.

There are better ways to do the same thing, such as using solid color adjustment layers and masks, but again I don't know your experience level.