I've been running Neima on veg for over 3 1/2 years.... running mostly wvo that I've filtered and adding some diesel in.
Winter can cause veg to thicken up as mentioned, but is fine once engine has warmed up.
Adding petrol will thin it, but be very careful to keep track if you put it direct into tank. Too much petrol can cause some nasty problems
As mentioned.. just start of with a few litres of veg from supermarket... this will help you get over the HOW CAN IT RUN hurdle...lol
I'm starting to stock pile my filtered veg ready for this years meets runs.... it's best to filter on dry winter days as it gets more out, especially any meat/chicken fats. If it'll go through filters in winter it'll be as clean as possible ready for summer..