For new parts: Denon SC-F109 (120€) and SMSL SA50 (70€). Of course, you will need speaker cables and a audio connector (probably a 3.5 mm to RCA depending on your setup and preference). Just make sure there is some gap between the rear side of the speakers and the wall. If you can extend your budget, you could also look into Magnat Vector 203 or a QAcoustics. Haven't heard them personally but I've heard good things about them.
In the used market, you have plenty more choice. First option that comes to my mind would be MB Quart 390 or 500 if you have the space.
No, the A500 replaces the Denon. Basically what you will be doing is: Compter --> U202 --> A500 --> Speakers
The speakers I linked to were on Amazon.de...but here are some other options:
Denon SC-F109: I'd go with these, personally
I just realized I didn't include any provisions for bluetooth, CD playback, and additional connectivity. For these I would grab an RCA switch so you can connect a TV or whatever other devices you would want. CD's aren't used all that much so that could be something left off because any CD music can be found in good quality online. But if it is a must then you will have to purchase a separate CD player. As for bluetooth there are a ton of RCA models so that shouldn't be hard to connect.