Connecting a headphone to an Android via bluetooth Please excuse a novice if the following questions are too simple are even stupid.

Question#1 As far as I know, *.aac generally achieves better sound quality than *.mp3 at the same bit rate. Even if I have an *.mp3 converted into *.aac, the sound quality will not be better. Is that correct? If it will not, why some take the extra effort in making such conversion?

Question#2 When I rip a CD track, I can choose the resultant format in either .mp3 or .aac. Is that correct?

Question#3 Suppose that both my phone and my headphone support {SBC, AAC, aptX}. How do they match? Do I have a choice to ask for a specific connection? [A simple answer (that does not include too technical info) will do.]
A rather simplified explanation of lossy and lossless conversion. 
Images: BMP and PNG are all lossless image formats. JPEG and WebP are lossy image formats. JPEG/WebP discard quality to become smaller. How? say a background is all black lossy duplicates RAW Data over the entire pic once rather than a continuous representation of 9 zeros. Instead 8 are missing but are still represented by the digit 9. MP4, WMA are lossy conversions for film, usually used for the Web, creating a small compact file using the fore mentioned data loss, by replicating the background rather than leaving it RAW.
Audio conversion: 
WAV, is a container file often used to contain lossless audio, although it is capable of containing lossy audio. 
FLAC is lossless, MP3 is a lossy audio format. 
Lossy audio files use the same premise as JPEG/WebP,MP4 WMA image conversion; 9 zeros can be compressed by discarding/throwing out 8,then using the digit 9 to represent all the zeros. Lossless files contain all 9 zeros and fit into the file size with out discarding/throwing out any of the zeros representing the RAW data. 
Ex&lt; a FLAC file only supports 24 bit audio conversion. A WAV 32 bit PCM audio file converted to FLAC would result in discard/throwing out some data.
ACC/MP3 like FLAC and MP4/WMA are lossy. No lossy Audio format is great according to my Audiophile roommate, I don't really hear a difference in quality between lossy and lossless other than decreased volume in the prior mention format. In Film it's clearly evident by poor quality in movement/pixilation. 

I hope I haven't confused you more, LifeHack or howtoGeek.com have a plethora of info on this one format VS format/conversion. 
As for your Bluetooth pairing/compatibility query. 4.0 needs to pair with 4.0 and so on. Follow manufactures pairing instruction. Ex; Its a myth that BEATS SOLO 3 wireless won't pair to Android devices and pair only to iPhone, simplifying it they discover one another because the "pairing Frequency" is the same, as in  4.0 to 4.0   

https://www.howtogeek.com/200698/benchmarked-whats-the-best-file-compression-format/

https://www.bing.com/search?q=geek.com+audio+and+film+compression&amp;FORM=AWRE1

https://www.reference.com/Bluetooth Pairing

Author: Chris Hoffman