This will be a kitchen remodel, with new cabinets. what is the smallest space, to conserve counterspace, you would allow if it were you remodeling?

absolutely take advantage of the depth of fridge and adjacent wall and insert something like this. you can configure these any way you want. I think this one is 12 in wide.

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It depends on the model.

Take a look at the Installation Instructions for GE bottom-freezer (including French door) refrigerators. As shown on page 20, a 36" refrigerator requires 43-3/8" to open both doors 90 degrees and 54-13/16" to open both doors 155 degrees (maximum). You have to check the specs and installation instructions for the product you're considering.

"what is the smallest space...you would allow if it were you remodeling"

If you allowed for a 33" French door, 18/19 cf GE refrigerator you could have as little as ( 48-3/8 / 2 ) - ( 33 / 2 ) = 24-3/16 - 16-1/2 = ~9" between the refrigerator and adjacent wall and still open the door 155 degrees.

What's best? Don't put the refrigerator adjacent to a wall.

It really depends on the model. Start looking up some different models in your price range and download the specs and installation sheets. My subzero had very minimal door swing needs because they have special hinges. It is a $10k+ fridge. Don't know if that is in your price range.