my light hearted, but snarky comment:
Napoleon would not start another war. We're told constantly that it was the coalition forces that forced the wars on Napoleon
My opinion is that Napoleon always planned a dual Spanish/Portuguese invasion. Spain originally didn't want French forces crossing, but Nap told them either let them across or be invaded themselves. French forces were barely on Portuguese soil before the 'reinforcements' going through Spain started taking over Spain. A Portugal only scenario could be done, but inevitably there's going to be friction between Spain and France. Spain would roll over constantly trying to appease France, and the country folk will rebel. I don't know if Nap has the fortitude to not take advantage of the situation. I seriously doubt it. IMO, the only way to avoid the peninsular war is to leave Portugal alone. Perhaps have Joao in Portugal roll over and capitulate to France, thus preventing the excuse for invasion? Of course, Britain then cuts off Brazil (Britain treated Portugal as an ally only marginally better than France treated Spain)
Austria was at a point in 1809 where they couldn't afford to keep their (still modernizing) army mobilized without a war going on. They were vacillating between attack or demobilize, when the situation in Spain convinced them to attack. Without Spain, I think they demobilize.
You probably see a couple of years of quiet time in the War (in reality, the only war going on at the time was Britain vs Spain/France) then it heats up again when Russia leaves the Continental System.
Britain was planning on an invasion in Venezuala for 1808 (led by Wellington) when the situation on the peninsula diverted them there.