Depends on which style of barley wine you're going after... If American, then you want 50-120 IBU. If English, then 35-70 IBU... I would suggest reviewing the BJCP style descriptions and then pick which you like better.
If you're mashing the grain, then plan on lower efficiency than you normally get. If you're using extract, then all bets are off. You could hit the OG, but have a much higher FG than you want.
I'm plugging in 65% efficiency right now for my barley wine recipe. I'm not planning on using any extract in my recipe. Right now, that means using about 27# of grain (total, 25# 2 row) to hit close to 12% ABV...
As for the dates... You might want to hold off on that. I would suggest using grains and a yeast that will give you the same kinds of flavors. Much easier to control. Otherwise, just crush the fruit, adding it during the aging process and getting off of it once it hits the desired flavors. I would plan on that being a short amount of time. You also might need to age for more time with the fruit addition.
What yeast are you planning to use? Have you done anything close to the OG/ABV level yet? If not, probably a good idea to do a couple close to that target first. I plan on doing a couple in the 9-10% range before my barley wine. I've already done up to about 8.5% so these won't be too much of a stretch. It will also allow me to get a better idea of the efficiency I should see (roughly) with the big brew...