[faint]

I'm still not sure whether this can be a really sustainable investment (reads: I would really use it beyond the initial rush).

I'm also wondering whether I shall start with the basics or - because if this is going to be a thing - with something that provides a little more.

A basic thingy would be a "Star Adventurer Pro" 
https://www.youtube.com/watch?v=JIwuidp9rCs
or maybe this
https://www.skywatcherusa.com/products/eqm-35-mount

I still have the old EOS 5D II which I could convert to Astro - although I may do that later on really.

I suppose that the start would be about some ultra-wide landscape shots and 300mm-ish nebulas.

Now ... can somebody talk me out of this to order to keep my sanity or tell me that this is not a stupid idea? ;-)

My condolesences to your financial freedom.

[toni-a]

Shooting landscape with milky way is something and shooting galaxies and nebulae is a totally other thing.
For the milky way yes add a decent fast ultrawide a good trigger and you are done.
For nebulae and galaxies things get more complicated, with a simple telescope earth rotation isn't your friend
Classically the rule of 500 ( shutter speed 500/focal length for full frame) is used to calculate shutter speed and avoid star trails it's equivalent to 1/focal for handheld
for a 20mm lens full frame 500/20=25 seconds that's feasible for telescopes you can't use 25 seconds so an expensive motorized equatorial mount is a must, it will compensate for earth rotation and allow longer shutter speeds , buying just a cheap telescope is just like buying Canon 75-300 lens, either you drop photography or you resell and buy decent equipment.
I did very little astro but my friends who do sometimes spend several nights for a single shot, shooting the nebula several times then stacking the pictures to reduce noise, they say it's a very rewarding experience

[Klaus]

I'm still not sure whether this can be a really sustainable investment (reads: I would really use it beyond the initial rush).

I'm also wondering whether I shall start with the basics or - because if this is going to be a thing - with something that provides a little more.

A basic thingy would be a "Star Adventurer Pro" 
https://www.youtube.com/watch?v=JIwuidp9rCs
or maybe this
https://www.skywatcherusa.com/products/eqm-35-mount

I still have the old EOS 5D II which I could convert to Astro - although I may do that later on really.

I suppose that the start would be about some ultra-wide landscape shots and 300mm-ish nebulas.

Now ... can somebody talk me out of this to order to keep my sanity or tell me that this is not a stupid idea? ;-)

My condolesences to your financial freedom.

We are talking about an (additional) investment of USD800-1200 here  ... or the price of a mid-grade system camera ...

---

1. Do you have easy access to place with  low humidity and/or  high altitude?
2. I assume that you can find place with less light pollution, Am I right?

Well, I'm living in Sydney and within the city limits, you can forget about astro photography, of course.

However, I don't really have to go far ... 
https://www.lightpollutionmap.info/#zoom...TFFFFFFFFF
(compare this to Europe ...)

And on the other side of the blue mountains, humidity is not an issue. Conversely, droughts are.