[Any advice on painting MDF terrain?]

Agreed with Spears. Enamel primer + paint combo is the best bet. I did that for all my Infinity terrain and it was the best way to do it.  No sealing needed and it doesn't absorb it up like normal primer.

[What % of the armies you regularly field are painted?]

Er, I don't think I've ever had a 100% fully painted army on the table.

Well, except when I used to run the Easter Egg Menites and brought them to GenCon 2006. Ha.

I also don't know if I've ever faced one.

[How many warbands do you own?]

6 in a short amount of time.

Bought Shadespire about a week-and-a-half ago for $60ish.

Played with wife a couple times. She sent me out to buy two more warbands so I bought skaven and skellies.

Then bought Nightvault this past weekend.

Loving it so far.