I use sand to build up the bases- often multiple layers, when the stand is thick (the Skaven stands all seem to be very thick).
I'd like to add flock, or some similar detail, but haven't decided on what yet. It'll have to be scarce, as the models are pretty crowded (I'd recommend 5 stands per base for anyone starting off with Skaven).
I chose clan Mors for a few reasons:
1) It's the largest, most powerful Skaven warlord clan, with no single association to the main clans, so it has a large amount of special units from Skryre, Pestilens, Mulder and Eshin. It's own warriors also tend to be fairly elite, as they frequently fight the Dwarfs and Night Goblins at Karak Eight Peaks.
2) The colours and rune of the clan are simple. Colours are white, red and black, and the rune is a modified 'M'.
3) They have no bizarre defining feature like some clans- no albinos, no dyed fur, no docked tails, or anything else needing modelling effort I don't want to put into the rats (I'd go mad with the numbers!)