I love my Flow hive, but they are expensive. The Western Red Cedar (WRC) is beautiful, and much lighter than pine. That makes it much easier for me to lift compared with pine, which weighs about 50% more for the same volume of wood. However, WRC is pricey wood, so the hive will cost you 2 or 3 times that of an equivalent pine hive. For me, it is worth it. You have to decide whether it is for you. The flow frames are very convenient if you don’t have an extractor. I actually do have both a centrifuge and a crush and strain system. I prefer the Flow frame extraction for the benefit of keeping the sticky mess outside, and minimizing honey losses from uncapping etc.
Some bees take to it right away, others have been reluctant. Many Flow users have found that brushing on melted wax, or rubbing some excess burr comb onto the frames helps a lot with speeding up acceptance by the bees.
I would suggest two, as others have said. More than that could be overwhelming at first. Fewer than 2 means that if you lose a colony, you have a 100% loss and have to start over. With a second hive, you may be able to recover by splitting etc.
Depends on your preference. I kept it simple. All of my hives are 8-frame Langstroth, because I really can’t lift a 10-frame deep box. So I got the 6-frame Flow super. You could go with a hybrid super, but I prefer to keep it simple and have the super all Flow or all traditional frames. You only need one Flow super per hive, as you can harvest on the hive, and let the bees re-fill it straight away.
Depends on finances and your tolerance for sticky messes! 
If I had unlimited resources, I would choose a WRC Flow hive every time. If you don’t do that, you will have to buy some kind of setup for extraction, or go with comb honey.