I only use 1 pole. I find having two is only really helpful on long walks on landrover tracks - gives a bit of extra drive. Having two on steeper slopes just trips me up. And if you're contouring, one pole is always going to be far too long unless you adjust it, which personally I'm much to lazy to do!
As for grassy slopes, they can be a bit dodgy when there's been so much rain. My brother had a nasty slip on grass on Sgurr Mor in the Fannaichs, when the broken pole he had found at the summit and insisted on taking home provided him with an ice-axe style brake and may have saved his life!
Might be better off with crampons and axe!
Steep descents? I'm with Kinley - zig zag. Also make sure you have decent tread on your soles, there's nothing worse than losing confidence in your boots when making a steep soggy descent.