Short, so as to not counteract the purpose of the sinking line and to allow you to be more directly in touch with your fly. 4 feet is a good starting point, maybe even shorter depending upon conditions.
I'd say tippets should be 2-3X for the larger flies in your size range and no finer than 4X overall.
Finally, a good way to fish streamers in still water on a sinking line is to construct your short leader with say a single or at most two step downs. Remember, you are using a shorter leader and it will not be as critical in turning the fly over as when you fish a dry fly or a small nymph. So, for example, a 4 foot 3X leader could go like this: 18" of .013 for the butt, 12" of .010 for the midsection and 18" of .008 (3X) for the tippet. Actually, come to think about it, it doesn't even need to be this complex... You could make the whole thing just from your chosen tippet size and be fine.
