Grease and Dust on linear rails

Hello All,

I built a router table that I use for cutting material for furniture
building (approximately 2 foot by 4 foot cutting area).

I am using some 20mm NSK linear rails for two of the axes. I was
wondering about lubrication for the rails, i.e. what kind of grease
to use, and how often is it appropriate to lube?

Additionally, I am cutting alot of MDF which produces a lot of very
fine dust. I have a vacuum collection system that collects much of
the dust, but some gets on the rails and ballscrews. I was
wondering if someone could comment on how harmful this would be to
the blocks and rails and if I should try and eliminate any dust from
reaching the rails.

Thanks,

Ed