Hi Justin,
A - No. To the contrary, Future will protect the paint (by the way, what kind of paint are you using?). I always protect my paintjob with Future (Klir in France) before masking. It also helps to avoid the silvering of the decals.
B - This is a matter of personal taste. While I would avoid a glossy finish in any case on a WWII aircraft (unless you have a reference photo showing the contrary), I would say a satin/flat finish is the best but some prefer a dead flat finish. I use a mix of Klir with Tamiya Flat Base (X-21) for my models:
- 100% Klir = Gloss
- 90% Klir + 10% Flat Base = Satin
- 80% Klir + 20% Flat Base = Flat
It is important to always test the mixture before applying it to the model. It is also important to stir up the mixture because after a while, the flat base remains at the bottom of the container. If you add too much Flat Base, the finish will be "milky" which is not very nice...
Jean-Luc