If you're shooting for 80VG then I'd recommend getting the nic in VG base. It's thicker and harder to draw into a syringe but if you have a high total % of flavoring (which is PG based for the most part) then it would likely
throw off your percentages and might make it difficult to actually reach an 80% VG. As far as what nic level to get, it's totally up to you. Many beginners start with 48 or 72 mg/ml nic since it's a little safer to work with than 100 mg/ml nic. In the long run, the 100 usually ends up being a little cheaper since you use less of it.