I'll also be taking suggestions as to who will lead the expedition to Ireland, as well as how large the expedition is.
In all honesty, I don't see why the French would not just do what they did IOTL and have Lazare Hoche lead the expedition. ITTL he has already established himself as a highly capable general, even though he is not exactly on the best of terms with the likes of Saint-Just and other radical Jacobins (though if anything, Hoche's enemies may support having him lead the expedition if only to get him away from the Metropole). In terms of naval leadership, it also makes sense to go with OTL's choice of Monrard de Galles, given that he seems to have been a capable leader. Indeed, the failure of the expedition OTL can mostly be attributed to the rough winter of 1796-1797, which led to the French fleet being mostly destroyed in a storm. If ITTL, the expedition is instead launched at the end of 1795, a year earlier than OTL, this problem will likely be averted, especially if the expedition is launched in
October or November Vendemiaire of Brumaire rather than in
December Frimaire.
With regard to numbers, IOTL the United Irishmen requested a smaller invasion force of around 15,000 men, arguing that they could potentially raise up to 250,000 volunteers on Ireland once the French had landed. However, I personally would advocate that a larger force of 20,000-25,000 men is sent, as Hoche had originally planned for IOTL, both to guarantee the success of the expedition and to allow the army to invade mainland Britain from Ireland.
In terms of targets for invasion in Britain, I see that you have already described plans for a larger-scale version of TTL's Invasion of Fishguard. As other diversions, you could also have invasions landing in Cornwall (this was proposed IOTL but called off due to concerns about soldiers' lack of discipline) and potentially near Liverpool (to take advantage of Northern radicalism) with the bulk of the Army of Ireland invading the Scottish Central Belt. If the Batavian Navy is in a better shape than OTL, you could also see invasions of Newcastle (again, briefly considered IOTL but dropped due to concerns that it would fail), Eastern Scotland (to better support any rebellion by the United Scotsmen) and, if the
Nore mutiny still occurs but is more successful, potentially even near Southend.
What happens next is pure conjecture. An (admittedly very unrealistic) idea that I have toyed with in my head is that the dire economic situation that TTL's Britain will soon find itself in leads to the Whigs under Charles James Fox win the 1796 General Election. However, his attempts to seek peace with France causes George III to attempt to dismiss him in favour of a Tory government which will continue the war at all costs. This triggers violent riots and mutinies that spiral into a Second English Civil War, and the French stationed in Ireland and Scotland take advantage of the instability to invade deep into England. All going to plan, they are able to force whatever regime in in London to capitulate, effectively imposing a pro-French republican government at the point of a gun, or at the very least permanently knocking Britain out of the war.
Like I said, a very unrealistic scenario. That said, the economic crisis that would doubtless be unleashed by the fall of Ireland would likely cause the situation for the British to go very South very quickly. If Jefferson becomes the next US President, he may even take advantage of the instability to start an early War of 1812, which would likely be more successful than OTL as ITTL, the British would need to use their army far closer to home so would therefore be less able to reinforce their colony in Canada.
That said however, all of this depends on the French being able to hold Ireland once they have taken it (IMO if the French can land an army in Ireland while any revolt is still ongoing, they are essentially guaranteed to be able to take the island, especially if the United Irishmen can capture Dublin early on and thus prevent the British from reinforcing their troops in Ireland). One must bear in mind that the bulk of the population is deeply Catholic, and so the British may attempt to promote Catholic sectarianism in opposition to the anticlericalism of the French army Presbyterian leadership of the United Irishmen (Wolfe Tone was a Presbyterian). Additionally, I just hope that Buonarroti does not get too.... overenthusiastic, shall we say, during his war with the Papal States; if word of any major anti-Catholic atrocities makes its way to Ireland, it could be enough for Irish Catholics to rise up against the French.