1, a veriaty in the diet is always a plus , some greens , pleco chips , blood worms is a good for them to.
2, Yes still vacuum the gravel it gets full of waste ( putting it politely ) too
3, they are fine to trat with malafix, they have "armour" rather than normal scales , without going into great details its things like clown loaches you need to be careful about treating.
Thanks
Paul