Should we stay in Aix for 1 or 2 nights?--We are then planning St. Tropez for 1 night and then Nice for 2.
(We are planning 3 nights Paris, 2 Avignon, 2 St. Remy and 1 Gordes)

2 nights in Aix.

St-Remy and Gordes are very close to each other - about 20 miles. For me it wouldn't be worth packing up and moving for 1 night. Avignon to Gordes is less than an hour.

I visited St-Remy, Gordes, and Avignon while staying in Aix.

That's a lot of packing and unpacking and moving around in a fairly small geographical area. But to answer your question: 2 nights.

I would limit my stays in Provence to two places at the most, given your time frame. Don't get the night in Gordes at all.

But as for your real question, who knows, it is totally up to you. It doesn't seem to affect your other plans, you didn't say it would mean taking a day away from nice, so stay 2.

Thanks. Two nights in Aix it will be!
While I agree that it is a lot of moving around and I usually prefer to stay in a place longer, the reason we want to do it is: we like to explore the restaurants in an area and have dinner without having to travel at night. We also like to experience the feel of a place in the evening, after the day trippers have left.

So dinner experiences are worth spending valuable vacation time packing and unpacking and moving from one place to another? Are you doing Michelin restaurants or similar? Seems a bit extreme to me. But whatever floats your bâteau.

There are plenty of towns in Provence where you can walk home after dinner.

Assuming you can walk.

2 nights for the reasons StCirq said.