MXR headphone Amp Bluetooth mod

[Moartinz]

Hi everybody!
I am a bass player always on the move and I would like to build a good play-along headphone amp for practicing bass. I am currently using a Vox Amplug 2 Bass that sounds quite good. But it carries some useless functionalities (backing tracks, tempo regulation) and also some mayor design lacks (direct plug, non rechargeable battery, line aux in).

Therefore here I am asking for your help for building a new device for replacing it once and for all. I hope this thread could be a development process where your knowledge can help a noob like me starting his adventure in the DIY pedal world.

About the the build:

1) AMP
From the countless nights spent studying this forum and the internet I have the sensation that the MXR replica is the way to go, with a LM386 chip as seen in GGG http://www.generalguitargadgets.com/effects-projects/boosters/headphone-amp/

Questions:
- Since a lot of years have passed from the design, is there anything better for this specific use-case?
- Can you help me understand how to tweak the circuit for optimizing it for bass guitar?

2) BT PLAY-ALONG
For the playalong functionalities it would be awesome to have a bluetooth receiver module for streaming backing tracks stored in my phone (that has no headphone jack) or computer.
Correct me if I am wrong but with a bluetooth receiver module like the M18 https://www.aliexpress.com/item/1005003575010329.html I should have an already amplified signal, so I should be able to wire the output directly to the headphone jack.

Questions:
- Has anyone tried something similar, and experience noise/interference with the AMP circuit?
- Is there any circuit recommended for blending correctly the sound from the amp with the one from the bluetooth?

3) POWER SUPPLY
Finally, it would be great to have a 9V battery that could be recharged with USB-c (that could act also as direct power supply). In order to achieve that I was thinking about getting something like this https://www.aliexpress.com/item/32992163327.html extending the micro USB input (and the LED) on the battery to the device enclosure.
I will also add a Buck converter (step-down) like this https://www.aliexpress.com/item/4001135296291.html for providing a stable 5V to the bluetooth module.

Questions:
Am I missing something?

I really hope to receive you guidance, ideas and points of view in this journey, Thanks everyone in advance!



P.S. Just a few ideas of what I have in mind