You are going in to a situation where maybe everyone is not an experienced player. That is ok, but your job might, on occasion, be about holding things together rather that laying down the funkiest grooves. And that is OK as well because the music is there to support not to shine. Not all keyboard players understand slash chords so C/E might well be read as a C chord and your playing the E could sound pretty muddy. The comment about pianists and looking after the bass end is completely valid - and sometimes it is just too much agro to educate them so you will need to pare your parts right back to not get in the way. There are all sorts of valid arguments about educating them, but in the heat of the moment they might forget and then it is your job to make the band sound good. You are there to enable the congregation, and that is cool. I could go on about this stuff all day!