Bicycle Mechanics - Part Replacement Basics (and a motobecane super-mirage)

Bear with me, I'm a mechanics noob. I'm looking to do some repair work on a (thus far not purchased) bike. I've been taking components into account, but I'm probably going to want to replace parts (cranks, shifters, whatever needs it). I'm wondering how easy it is to switch brands...

As an example, I'm looking at a 1980s motobecane super-mirage, which has suntour hubs. I've heard it's tough to find suntour parts. Can I just replace the hubs with shimanos or srams? And the rims are Weinmann, which again I've read bad things about. But I've heard older rims are oddly-sized (at least compared to available rims today) -- would it be hard to find decent replacements for the Weinmanns?

In general, are there particular brand components that are easier to replace, and are there certain parts that are tricky size-wise?

If you have no experiance with fixing bikes, getting a old one with a lot on known issues is not the best place to start, from all you have listed you want to replace, the crank and shifters are the 2 most expensive bits on a road bike after the frame / forks, you may find the cost of replacing these is more than a new / nearly new bike.

Hubs, these will be 126mm, obsolete as road hubs are now 130mm, the frame can be cold set to take newer hubs, the biggest problem with be the suntour are freewheel, all Shimano and SRAM are Freehubs, and use cassettes.

Nothing wrong with Weinmann rims, but may be 27", current now is 700c.

Think you may find it easier to buy a current bike, an 80's bike will also have compatibility issues with the headset, being 1", the gearing, most bikes are now at least 9 speed, with 10 being most common.

For compatibility, this used to be easy, but now the same manufactures groupsets are not always compatiable one year to the next, so very hard to know without knowing what you were looking at.

You can still get parts for older bikes, but you will have to hunt for them, it's easier to have a current bike where any part required can be purchased off the shelf than having to hunt on ebay or a HTF part

Depends on your objective. If you just want a functioning bike, parts should be pretty cheap. I'd just replace the whole wheel rather than hubs or rims...but I wouldn't replace them until they really need it. Things like the bottom bracket could be tricky on an old french bike - bb might be french or swiss threaded making it impossible to get new modern parts for it.

If you want a bike with modern parts, it will be a real pain. Would probably be cheaper just to buy a new bike.

You need to post your question in Classic and Vintage. The responses will be completely different and much more helpful.

I love old French road bikes. I have four.