Playing as accompanist musician - Challenges

Intro -

I get asked to play alongside with pre-booked bands for weddings or church events. I often come across the following challenges and I would like to know from fellow musicians how you deal with these situations.

Key of the Song - 

I get to play  7-8 songs along with the choir team or the band. I come in early, sit with the pianist and ask for the key of each song and I make notes on a notepad. However, at times the pianist is busy or the key is not decided or a song is played on spot without prior heads up. This is when I get stuck. How do you overcome this situation? I would like to be independent and learn a way to identify the key of the song myself.

Mic Setup 1 -

Currently I use Rode Wireless Go 2 with Lav Mic. Transmitter is clipped to my shirt and the Receiver is connected to the Piano Mic Input and I ask the Pianist to add a Reverb effect. Using a wireless mic helps me move around. However, since I do not have the control, I'm dependent on the Pianist. Also, at times my Harmonica sounds squeaky on high notes due to some incorrect EQ setting on Piano. How do you all manage this scenario?

Mic Setup 2 -

How do I get the a fuller and fatter tone on the Harmonica? What's your Mic EQ and Effect settings :) and what's your portable mic,amp,effects setup :)