Europa Universalis 3 - Page 47

Excellent Shipwrights (+2 Leader Maneuver) -- This one is hugely important. Fleets with a 6 maneuver admiral don't take *any* attrition!

Military Drill (+1 Land Morale) -- This is mostly an early game NI, but is still extremely powerful later on in the game. It should make your units have around 1.25x the morale of someone without it in the era where you are, which can and will make the difference between winning and losing an otherwise even fight.

National Conscripts (+50% Manpower) -- This one is pretty much as important for land as Excellent Shipwrights is for Naval. You can and will run out of manpower, and even if you can afford an entirely mercenary army (odds are you can't) mercenaries aren't as good as regular troops (for example, they miss out on Military Drill).

Press Gangs (-50% Ship Cost) -- You may be rich, but so are your opponents. Since the number of vessels you field isn't limited by manpower, this means you will be able to sustain around 1.5x over your forcelimit for the same price, not to mention making replacing vessels cheaper.

Engineer Corps (+1 Leader Siege, +25% Defensiveness) -- Level 4 forts are nasty not to mention Level 5/6 (if your opponent chooses to go that route), and an extra point of Siege on your generals will help immensely. The defensiveness is nice too.

Espionage (+1 Spies/Year) -- If you lack natural spy gain this is a big deal, and maybe even if you have spies already but want more. Funding rebellions in hard to reach places is one of the easiest ways to make an empire collapse.

Vetting (+ 33% Spy Defence) -- Helps avoid the above, especially if you went Free Trade. You have no idea how damaging spies can be until you experience them from multiple rich nations at once. Also, make sure you have a Cathedral in your capital for the extra spy defence, since the capital-specific spy actions can be really nasty (especially Infiltrate Administration).

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NIs to avoid unless you have free slots with nothing to use them on:

Regimental System (-20% Regiment Maintenance) -- This one is for smaller empires with better infrastructure and less obscene colonial income. You will run out of manpower long before you run out of money, so unless you have a free NI you're much better off with Press Gangs.

Seahawks/Battlefield Commissions (+1 Naval/Army Tradition respectively) -- In a world war you will maintain so much tradition that these NIs won't help; they're mostly for keeping your tradition up during peace time.

Superior Seamanship (+1 Naval Morale) -- More morale for your navy is nice, but I assume you still want some economic ideas and this isn't a huge deal.

Glorious Arms/Naval Glory (+100% Prestige from Land/Naval battles respectively) -- Prestige is nice but the other stuff is better.

Naval Fighting Instruction (+50% Blockade Efficiency) -- Not as powerful as it sounds.

Grand Army (+33% Land Forcelimit) -- Helps a bit in that you will have a bit more manpower overall (33% more fielded initially, that is), but in a long war that will be rather insignificant and there are way more important things to spend a slot on.

Grand Navy (+100% Naval Forcelimit) -- Do you really need more ships? I'm guessing your forcelimit is at least 500 already.

As for the game getting easy, that's kind of inevitable in SP unless you constrain yourself. Settings like Low AI Aggression and Lucky Nations can really help to make the AI harder to deal with (Very Hard as well but it doesn't have anywhere near as much of an effect as the other two), but you might also want to set some constraints for what you're allowed to do; for example, I'm playing a Low Aggression game as Sweden where I was only allowed to conquer my starting cores (Skane, Halland, Jamtland if I recall correctly), any cores I was given from missions (Estland, Livland, Riga, Kurland, Vorpommern), and the finnish territory that Sweden realistically took from Russia (Kexholm, Neva, Ingermanland). No vassals except those that encompass only territory I'm allowed (for example Finland, Kurland etc) and no PUs except if they naturally happen (no Claim On Throne, no Forged Documents, no War of Succession). Any inheritances need to be sold as soon as possible. It's in the mid 1700s right now with a Big Blue Blob that stretches from the north half of Iberia all the way over to the north half of Italy, Great Britain and Spain who've colonized half the known world, an Ottoman Empire which has eaten up basically the entire middle east, part of the balkans, and all of Saudi Arabia, and a bunch of small but powerful states like Prussia, Austria, and Bavaria. I managed to get PUs on Austria (inherited then released), Netherlands (who is the strongest colonial nation and would be even stronger if they hadn't been PUed for over 200 years now), Pommerania, and The Hansa (they became an administrative republic then an administrative monarchy for some reason) without even trying; it's surprising how many PUs you get with decent prestige, high relations, and no claims. Anyhow, it's certainly a lot harder this way, but still surprising how powerful you can get; I don't even have enough provinces to declare myself an Empire, but I am ~50 tech levels ahead (when combined, so 10 in each) of the next nation, have a force limit of ~350, a naval forcelimit of ~150, ~600,000 manpower, and ~5,000 income according to National Statistics (next is the BBB with ~4,500).