So the consensus of the forum seems to be that raising a fleet to successfully challenge RN supremacy in mid 1810s and try an invasion or blockade of the British Isles takes far too much time, effort, and difficulty for the Napoleonic Empire. Well, this dovetails with my own tentative feelings of the issue, that a late Napoleonic Sealion was not a realistic scenario. It is far more likely that Britain and Napoleon make a reluctant peace after total victory on the continent. Nappy would not see invasion as realistic, and Britain would see that they can't really defeat him without allies on the continent (plus war weariness would affect Britain, too).
To comment on some other points that have been made:
You would need to define further what you meant by wiping out the Austrians and Prussians. Do you mean dismantling them as nation states or simply significant military defeats that shatter their armies and render them impotent for a number of years. For the later, i'm thinking the Austrians between Austerlitz and the rematch at Aspern Essling and Wagram.
Since I'm persuaded that total dismantling of Prussia and Austria was all but necessary for the long-term success of the Napoleonic order, assume the former. See
here for my ideas on the issue.
Also, crushing the Spanish insurgents will not be an easy task, the French army pretty much lost control of the countryside very early on.
Well, the Napoleonic army had regained a fair degree of control in the Iberian peninsula during the time Napoleon
gave the area his undivided attention, so I assume that once Russia is defeated, and the Empire can give back its main focus on the area, the guerrilla can be eventually defeated.
Furthermore, Napoleon himself will have to come forth to defeat Wellington.
Bah. Wellington almsot got his butt kicked if Blucher had not saved the day for him, and ITTL he would face a much stronger Grande Armee (and a less exhausted Napoleon) than at Waterloo. I have little doubt on the outcome of of the confrontation.
The sensible option here would be to make a permanent peace with the Brits and try to persuade them to accept French continental mastery.
This was also my tentative judgement, but I had to seek a second opinion.
Given that Nappy has established His Empire, and pacified Europe, ?Would France develop a RN equal Navy?
Even after 50 years of calling for a Navy equal to the USN, the USSR never did.
The French would concentrate on its Land Forces. While the Empire would have a Navy for Pirates, and such. ?Would it try to compete with HMRN?
OTOH, the Empire would span France, the Low Countries, Italy, and Germany, which are best described as either navel powers or land powers with a sizable naval leaning. The Empire would need very strong land forces to keep Russia at bay, suppress rebellions, and prevent british encroachment on the continent.
But I find it very difficult to believe that late Napoleon and his successors would concede unchallenged worldwide naval supremacy, i.e. control of global trade and colonization, to Britain. In this sense, even if I easily accept that Napoelon would shun trying a Sealion, I do not find realistic that a stabilized empire would neglect building a Navy competitive with the RN, from the late 1810s-early 1820s onwards.