Swapping Stony Substrate For Sand...and Adding Molluscs

[xpeterpx]

I have an established tank with 3 Gouramis,2 Plecos and a shoal of 6 Neons.- basically not a big tank of around 76l.
I'd like to know 2 things..
-Firstly am i likely to encounter many issues swapping my stony/pebbled substrate for sand with this stock

-Also I'd like to add 2 Molluscs as cleaning patrol.Are these good community additions or should I steer clear?Any likely issues etc../

Thanks as usual
Pete