I would use a starter. Using Beersmith it suggests around 850ML starter if you use a stir plate. If not then you would need about a 1.4 L starter I usually make mine 36-48 hours a head of time. But have done it as little as 18-24 hours with good results.
Always a good idea to make a starter for liquid yeast.
Yes, I would make a starter. I'd use mrmalty.com or yeastcalc.com to determine the starter size. I like to give my starters two days, then I chill, decant, then pitch the yeast slurry. The dacanting step is optional, many just pitch the whole thing.