I'm not a fan of Aluminum wiring. And don't assume that 6AWG Aluminum is the equivalent in copper. I'd suggest replacing, if possible.
As to the breakers, age isn't that big of a deal, but then again, they aren't that expensive.
But I wouldn't (and the electrician probably won't let you, since there may be code issues) put the low voltage wires in the same conduit as the high-voltage.
Yep, second most of this. Assuming it's going to be inspected, your electrician should know what to do.
There's nothing "wrong" with aluminum for larger stuff like this, since you're unlikely to directly mate it with copper (which is where it's problematic in smaller applications), and most terminal connections at that size are Al/Cu ready. That said, 6ga aluminum in conduit could be touch-and-go codewise for the current capacity you need. Since it's so old, you probably can't easily reference the manufacturer's amp ratings, but based on the stuff they make today, even if the insulation was rated for 90°C (it probably isn't), it'd probably be a little undersized. I'll be surprised if your electrician doesn't replace it.
One other thing you might want to consider: if you're all-in on this EV thing and have to replace the wiring anyway, you might want to have him size the wiring/conduit for 100A@240V for future use (but still a 50A breaker for now). The Model 3 LR onboard charger maxes out at 48A today (if you were using a wall connector- less with the UMC it comes with), but your next car might not. The additional expense to bump the conductor size up is pretty minimal compared to what you're going to pay the electrician...
Oh, and I'd replace the breakers if it were me... You're going to be pulling close to its rated capacity constantly, and old breakers have a tendency to "buzz" for various reasons.
For the low voltage stuff: even though there are limited situations where it can be legal to share conduit, don't do it. You'll likely have to use a much more expensive low voltage wire to be code-compliant, and many inspectors just don't like it (even when perfectly code compliant). Plus, you're opening yourself up to all sorts of potential noise issues on the low voltage stuff with a long parallel run in such close proximity to high voltage AC.