As a commuter, it's not bad. The drivetrain should work pretty well if you can replace the chain and lube the hell out of everything (including the freewheel internals, which you can just drip lube in from outside).
With a bike of this quality, you're better off starting with what's there and only replacing what you need to. Brakes, headset, bb, shifters, hubs can all be disassembled, cleaned, re-lubed, and reassembled. Most of those parts should work quite nicely afterward.
That Crane rear derailleur though...that's way better than the rest of the bike. Replace it with one of these and then find a more appropriate bike to put it on. It's a very nice derailleur. You will find it in the original Dura-Ace catalogs - for whatever reason back then, the Dura-Ace line was all called Dura-Ace except for the rear derailleur, which was known as Crane.
Definitely possible, though your options are so varied that it'd be hard to list them all.
If it were me, I would get an inexpensive claw-mount rear derailleur to put behind the bolt on the wheel, and replace the rear wheel with a 5-speed 120mm hub (coincidentally the same spacing as modern fixies) and a friction shifter. Up front, a front derailleur and multiple-chainwheel crank would be possible.
Note, however, 120mm rear hubs aren't made new anymore. A 126mm rear hub (6/7 speed) can either be re-spaced to 5-speed for a 5-speed freewheel or if your frame is steel, the frame can be spread slightly to 126mm.
The latter option would be very smart, because Shimano still makes an excellent 6-speed freewheel (5sp only by other brands) and gives you the potential to index with a modern 6/7-speed compatible shifter.
The internally-geared hub option is also very smart, assuming you are able to lace one in, and would maintain the aesthetic and maintenance of the single-speed a lot better.
That rear derailleur looks like a Huret Eco (or Sachs-Huret or any other similar design).
It's flaw is that it actually swings away from the cogs as it swings outward. The further away it is from the cogs, the worse it will shift. That particular derailleur ends up so far away from the cogs in top gear that there are 5+ links between the jockey wheel and top gear. It shifts horribly in those upper gears. It's also more likely to have the chain overshoot.
Literally this would work a lot better. And I realize it looks very similar in operation, but because of the way the pulley cage is designed (location of the pulley relative to the cage pivot point), it actually does do a decent job of maintaining clearance.
Look at your derailleur - the top pulley is mounted right where the pivot point for the cage is located. This is bad because the derailleur body's downward swing does not get corrected. I realize that's complicated, but just trust me that any derailleur you can find in a pile in a box somewhere is better than what you have. I also recommend a SRAM PC-850 chain for anything 8-speed or below.
What kind of upgrading do you intend to do? Modest and mostly period-appropriate, High-end and period-appropriate, or modern? I have a '74 Raleigh International that I did a somewhat resto-custom build on, using a variety of '70s and current parts that keep the character of the bike intact while ensure it performs well and doesn't leave me stranded. Somewhat a mix of the first 2 options.
If you're commuting I imagine you'd want to do something similar. I'd repack all the bearings with new balls and grease to start, true the wheels, replace the cables/housing, etc. For the drivetrain though, especially because it's plastic Simplex, it's historically significant but not good for long-term riding. I'd take them off and replace the rear derailleur with this, and the front derailleur with this. Both are dirt cheap, but would give very comparable performance to the original Simplex, with similar designs (I swear that F.D. is a clone of a Huret design) and similar appearance. I actually love that R.D., despite how cheap it is. For shifters, there are plenty of sources of bar-end, or you could switch to downtube; Huret made plenty of all-metal designs that performed very nicely, and would be appropriate on a French bike.
In regards to your crank issue; it's likely the rings are the only thing bent, and you could replace them. If you're a bit brave, you can actually unbend them with an adjustable wrench, time, and care. I've straightened alloy chainrings/spiders where they wobbled by a few millimeters, it's not as easy as steel but it usually works if they're just a little wonky. Make sure it's not just the bottom bracket wobbling though. That'll be cured just by a repack and adjust (above).
Overall, a lot of what you've got there is serviceable and can be brought back to a reliable state with a good day of tuning. The only thing I'd outright 100% replace and put on a shelf are the derailleurs, and replace that saddle with a new Brooks.