Hi Guenter, if your graphics card is still pending …
3 years ago, I got a big tower ( DARK BASE 900 | Silver leise high-end PC Gehäuse von be quiet! ) with i7-8700 + air cooler (Bequiet), Nvidia GTX 1060 6GB (activ cooler), power adapter (Bequiet) … It just fits under my desk with space all around (cooling system not obstructed), is really quiet and works for me (no gamer, no overclocking, stable drivers). And even in hot summer, I don’t see temperature exceeding 60 / 70 celsius, otherwise far below.
The modell GTX 1060 is already outdated, but instead you can get GTX 1660 or GTX 1660 Super (2 slots, check size …, 120/125 W max).
Of course there are faster cards, but they consume more power and produce more heat (see comments from Lucas).
have fun, Wolfgang
I would not hesitate to buy again. When running, the noisiest component is a 8TB data grave, while OS and scratch disk are M2.storage.