Do I need to apply future to my flat paint before applying the dry transfers?
No. The reason for a gloss coat under a decal is to prevent air getting under the carrier film and causing silvering. Dry transfers do not have a carrier film and can go right on the flat painted surface.
Do I need to spray a top coat of flat with future over the transfers to protect and help blend in?
Yes to the top coat but it does not have to be future. A top coat not only seals and protects it gives the same surface for whatever weathering you may do so the weather does not look different on the dray transfer form the surrounding areas.