Good questions.
1)The crown amp has lower distortion and lower noise floor(very important in an amp). Because they are well built to be tossed on tours and events, they don't have fancy looking plates, and anyone who says that the Crown XLS has no place in home,has never heard one. There are users around the world who have paired this amp with speakers in the range of 2 to 10 lakhs. Even sensitive speakers sing with it because of its smoothness.
You may want to read this one thread out of hundreds on the net singing praise for its musical abilities.
https://www.stereophile.com/content/crown-xls-series-any-good-severe-bargain-pro-amp
a preamp is what you need to control your source and volume. If you get something like the
Schitt SYS, around 6000RS, it's a passive preamp, it has two RCA inputs, and one RCA output that goes into the power amp. But then you will need a DAC (again easy to find something in your budget.)
You can plug a Bluetooth adapter, But Chromecast is better IMHO.
3) I think the answer is in the above point #2.
Now , When you buy an AVR ,You are paying for a lot of things that a stereo setup does not need, like HDMI connectivity, Dolby,DTS codecs, room correction software,and a host of DSP features that may or may not be used at all. So all these features are not needed when it comes to music only playback.