Referring to the several pinout pictures and schematics that have been posted here, I have some information based on my own experience with this little module. I am using the XS-3868 V3.0 board.
1) the R-C network connected to the RST pin is a reset circuit. It slowly charges the capacitor thru the 10K resistor, causing the RST pin to initially be "low" when the power is applied, and after a while, the capacitor voltage increases to the "rail" voltage, V1.8, and then it stays there. I have to presume that the RST pin is actually active "low" so when power is applied, the OV3860 stays in reset for a bit, then is allowed to run.
I have found, in my case at least, that this isn't necessary. However, it may need to be there for every unit to reliably come up.
2) I too have this "crackle" noise (sounds a bit like static or ignition noise on an old AM car radio) during the quiet/silent parts of the music, but as someone else has observed, just placing one finger on the little antenna trace area quiets it down to zero without affecting playback, at least no effect at the range of a few feet. I will have to experiment with resistor/cap networks to see if a sweet spot can hack this into submission without application of the finger!
3) this board is meant to integrate a LiION battery charger. That's what the Charge.Pwr pin is for; you put your charging voltage in there, and the chip will then supply charge current to the battery. Now, I didn't intend to use a battery, so I omitted it, but I did put the electrolytic cap as indicated. The cap ends up being the power supply for the whole thing, but your external power should go into the Charge.Pwr pin, not the V.Batt pin. I used 5v coming off a hacked USB cable, for convenience (you can plug it into a cell phone charger, your computer USB port, etc). This seems to work just fine! I think providing anything less than 5 volts to the Charge Power pin, and/or not including the large electolytic cap across V.Batt and ground, will cause the chip to not work correctly.
4) contrary to popular opinion, this little board both transmits and receives BlueTooth! The pause/play, next, previous buttons are part of the Remote Control profile. Implementing these buttons transmits commands back to the music source that you've paired to. However, it is true that this chip will only serve as a "sink" (ie, "receiver") for AADP (Advanced Audio Delivery Profile ?) aka A2DP, aka "playing your music from your phone to this little board".
That's all I know right now. Will post an update if I fix the static-y noise issue during silences.
~~The Night Squirrel