Nice looking bike. It's not so different from our '82 Peugeot, even to the double stays from HT to rear DOs. We picked it up in pieces and I rebuilt it over last year's autumn and winter. Because I had some of the original parts I wanted to maintain as much of its French-ness as possible, subject to it being a useful bike. So I'm reasonably familiar with what you want to do. I'll describe our experience and you can learn from that.

Over the last 10 months we've ridden ours over 1800 miles. We've climbed no mountains, but New England is very hilly in spots. Our longest ride was 62.6 miles, our typical rides are 40-50 miles, and 80 miles total each weekend. We did one overnight trip to a campground about 40 miles from home with the bike loaded to about 95lbs. I'm 63, and together we weigh only about 270lbs. So we aren't power riders but we've had great fun and have come to trust the bike. We run triple chainrings, 52, 38, 28, and I found a tandem-specified Suntour 5-cog freewheel, 14-32, so the gearing is good 1-1/2 step for both chainring shifts. Low gear is good for maybe 5.7 to 7.0mph. I would recommend you rig yours with conventional cranks and chains instead of both chains on the right, or the drive cranks in front.

Ours has the original Mafac canti brakes with Koolstop pads. it is rigged with the right Mafac lever operating both front and rear. I have adjusters on both cables so I can keep F and R balanced, but that isn't a big problem. The left Mafac lever operates the Atom drum, not strong enough to stop the bike but adding useful stopping power to the cantis besides acting as the non-rim-heating drag brake. Together the brakes stop the bike well enough but admittedly they aren't up to modern Tektro or even traditional Campy standards, which are VERY good.

VeloOrange BBs might make sense for you. I run traditional bearings in ours, but I spent a lot of time trying to find good spindles of appropriate length. If your bearing cups are in good shape and you have all the parts there is no reason for you to change them.

For wheels, the front wheel is easy, it can be most any "touring" wheel. Our was a custom wheel (built for someone else) on a Shimano 105 hub, A319 rim, and only 32 spokes. The rear is also a modern rim built onto the 36-spoke Atom hub. As long as your axle is straight and the bearings and brake pads okay you should be able to use them. String (or have a bike shop string) a new rim onto the old hub. That's easier than switching brakes and all that it implies. You DO want nice alloy rims spec'ed for strength, not for lower cost.

I run close-to-original Simplex derailleurs, believe it or not. The FD is a later triple model (I forget the name), and the rear is an SX810 (I think) with the long "GT" cage. They shift pretty well, but aren't Suntour-quality. I even have Simplex levers.

Part of your plan will depend on your bike experience. If you're experienced or at least comfortable working on bikes there isn't much to worry about other than finding missing parts. Part will depend on your weight. If we weighed 370lbs total I might worry about a few things. But if you can keep the bike in good shape it should be a good machine even if it isn't "modern". People will tell you otherwise, but our experience is that those were quite nice, functional machines.