ordering a la carte for wife, le menu for husband

Generally no -- it shouldn't be a problem, especially if your wife orders a plat rather than, say, just an inexpensive entrée.

We sometimes split a salad, for example, or share a plate of escargots with no problem.

Some fancy restaurants do have "menus dégustation", typically many many courses, that are meant to be served to the whole table (for service syncing purposes). But (1) the menu will clearly state so and (2) it's negotiable.

This is totally not a problem. My husband and I do what you describe all the time. He usually wants all three courses (or maybe even four) and I will often have only a main course. He usually offers me some of anything good that he has on one of his plates. This has never been a problem. I have always ordered either a main course or two appetizers. I think a place would only care if your wife ordered nothing or a cheap appetizer and then proceeded to eat half of your meal, which sounds highly unlikely. When we are a foursome with our two children, our daughter just about never has a first course (saving space for dessert) and again no problem at all. She and I just sit at the table and enjoy our drinks or eat a bit of bread while those of us (my husband and son) having a first course do their thing.

Each diner has his choice: ordering a menu (3 courses at a fixed price) or a la carte (at least one main plate). Tasting menus are typically only served to the entire table, everyone must order it.

Main courses are never shared. Desserts are often shared. First courses are generally not shared. French portions are much smaller than are what one typically served at US restaurants. Some restaurants offer menus with a 2 course option (sometimes referred to as a formule) which might appeal to your wife.

I was about to say that I agreed with the people who said it wouldn't matter; but then I realized that you were asking about a Michelin 1-star. In that case, I don't know!

Why not just email the restaurant and/or check the reviews, and questions and answers on TripAdvisor?

We ate om Chateau de Pray's wonderful Michelin stared restaurant. I had the multiple course priced price menu. My husband ordered an entree and dessert. It was no issue, they were most gracious. It's a wonderful splurge for anyone that is in the Amboise area.

It will not matter no matter the star level of the restaurant chose as long as you both order something. Restaurants know that some people eat more than others. The only time it might matter as mentioned before is if you tried to order the tasting menu for one at a place where all people at the table must order the tasting menu and even worse tried to split that single order between two people. Which is not to say that you may not be able to convince the wait staff to serve the tasting menu to one person and let the other order off the regular menu. I have been able to do that on more than one occasion.
Last April, my husband and I ate at Restaurant H, a terrific one-star place in Le Marais. We both ordered the tasting menu even though I knew I did not want two of the courses. My husband ate those two courses (and still claimed afterward that he was still hungry). Absolutely no problem. In that case, there is no reason for the restaurant to care because they have two covers and the patrons ate two meals. Unless it is required for a tasting menu, your wife can order to suit her appetite and you can order to suit yours. I would just be mindful of your wife ordering a cup of soup, for example, and then eating half of your meal. That will be tacky because really then what you are doing is taking up to seats but only ordering one meal.
A few nights ago, my husband ordered two starters and a main course, my daughter ordered a main course only, my son ordered a starter and a main, and I had a main course and a dessert. The waiter brought out all three starters. My daughter and I both had a second kir royale while the males ate their starters but we could have just as easily had water. Then the server brought all the mains and we all ate. Then came dessert. I ate mine while my husband had a coffee. The children decided to leave us then and walk around the Haut Marais neighborhood and meet us later. The point is that you don't want the staff to feel like you are trying to take advantage of them just as you do not want to feel taken advantage of by a restaurant. Just bear that general principle in mind when ordering.

We commonly order 2 courses -- my husband the entree and plat and me the plat and dessert -- and share the outlying dishes slightly. We have when ordering a salad to share had the restaurant actually plate it for two. Some restaurants are very good at sharing entrees and desserts (never main courses though) Chez Dumonet encourages this for example -- we had a waiter tell us that the foie gras pate starter would serve all 4 of us just fine and it did and people usually share the souffle for dessert or the giant millefuile.

Some restaurants only have a menu and one must order the menu. Some require everyone in the party to take the menu if one does.

Everyone needs to order a main course not just an entree at a restaurant although when having dinner with a young child, it was fine to get her an entree instead of a main course -- you wouldn't take a small kid to a restaurant where this would be an issue though.

Thank you, one and all! We're getting our appetites ready....

We did that at a chef-owned 1-star: husband had the menu but I ordered less à la carte. However, being a classy place, they sent out a little vegie pâte for me while my husband had his first course, explaining that I shouldn’t have an empty plate while he ate. A less considerate restaurant might have let me sit there nibbling bread.

I would never even consider it an issue. While I pretty much always order a menu, my wife sometimes orders a la carte, although it's almost always the same number of courses.