Flat roofing/Insulation questions

I live in SW Florida, in an old house with an, almost flat roof. The cielings are on one side of the joists, and the roof on the other side. There is no insulation. Access to the soffets is not available to blow in insulation. On either side of the roof "peak" we plan on cutting out a 6" wide piece of roof decking, the length of the roof, and blowing in insulation, then reinstalling the pieces of decking, and putting a piece of rolled roofing over the "peak" to cover the work. We plan on replacing the roof in a few years. Questions:

Is it OK to have a 1/8" gap in the decking, where the saw cut was made? If not what should it be sealed with?
How should the rolled roofing be attached?
what should be applied under the new rolled roofing?
Is there a better product to cover the "peak" with?
Can a rolled roofing, roof, be coated with a product like Cool Seal? Thanks for any ideas, Can you guess, I'm not a Roofer?

I believe you would be better cutting a hole in the drywall and blowing the insulation in from there. I lived in an old farm house in Iowa as a kid. Dad paid some contractor to come out and blow insulation into the walls. They drilled I remember 1.5 inch holes in the siding and attached the machine. Replaced the plug and caulked. We painted the next summer.

I personally do not believe in touching flat roofs. As an electrician I have put ceiling fans in for people with flat roofs. Every one of the holes I drilled leaked. Every one promised that the roofer was coming next week. One leak was in a low spot and ruined the whole bedroom, the master of course. I do not cut holes in flat roofs for love nor money. Cool seal works pretty good for small infiltrations. Not a crack, not even a

1/16 of an inch. Rolled roofing is usually installed with hot tar. Big kettle thing that stinks to heaven.