Sennheiser - MKH 8020

That's a huge advantage to living in Germany! Also the older version of this mic is the Sennheiser MKH 20-P48. In 2017 I bought a pair. Now I have 2 matched pairs of 8020s which sound just as good but are smaller. I wouldn't hesitate to get a used MKH 20.

You mentioned the MKH8020s (I use those now; they're awesome and totally worth it), but the much more affordable Line Audio OM1s are also very nice omnis. I also have a Rode NT4 for a quick XY Stereo set up, and that's done well whenever I need it. Hope you find something you like!

Phew, depends on whole a lot of factors. For an easy-to-use and general purpose mic, I really think more people should try the Electro Voice RE50 (the 635a model was extremely similar, but is not currently available new). That's for more of an up-close spot mic that won't get overly boomy because of proximity effect and resonances coming off the guitar body. You may also be able to find a used clip-on DPA 4099 instrument mic in your budget. Remember to consider what would be comfortable for you to manage by yourself, if you're working alone. Juggling too much equipment can take your attention away from the instrument. For what I personally like to hear in a recording, my "favorite" would to be blend a spot mic (like the above), with a mid-side stereo pair of condensers. This is definitely more for a professional recording situation, but my favorites right now a Sennheiser MKH8020 / MKH8030 pair.

For quiet ambiences you are best off with low self noise mics. Omnis would work well in this instance, so perhaps mkh 8020 if you have the budget, personally I would go with the Rycote OM-08 and a Zoom F3 or similar recorder. I’ve use clippy mics for these instances but I still find their self noise of 14 dba to be a little too much for my liking. Obviously you could always just use two Rode NT1 in an ORTF setup but they are a bit bulky and not really intended for outside use. Their self noise is super low though so they would definitely work well

800 series are a bit shit, as is the 609 guitar amp mic. Unpleasant sounding in a way I find it hard to describe. The 945, however, is a very nice mic that I use a lot. It suits most voices pretty well, lots of clarity and nice pickup pattern.

I went to a Sennheiser backed mic shootout at a world class studio. I think it was a NARAS meetup. They had all the Neumann mics lined up along with the 8000 series Sennheiser mics. I thought the 102 sounded thin and harsh compared to everything else in the room. Most others there agreed. The most pleasant sounding mic was the M149. The most real sounding mic was the 8000 series Sennheiser. They were much more transparent than the KM184. I’d say on par with the B&K, now known as DPA mics.

You gonna need sensitive mics. So capacitor mic with small diaphragm like neuman km184 or schoeps cmc6. But that’s expensive. You can use shotgun but sometimes it will be difficult to have enough distance in a small room. Sennheiser have good shotgun (mkh series) and it’s cheaper than Neumann KMR or schoeps CMIT. But my best mic advice would be Line Audio CM3 are really cheap and sounds great.