Seems like everyone's too lazy to make a strategy guide, so I guess I'll make one. This is currently updated for K2
All sections past "choosing a starting base" will contain spoilers in a "least spoilers first" fashion. If I seem to be spoiling things too much for you, just skip over to the next section
1. INSTALLATION AND SETTINGS
Can't strategize if you can't play it. Read the readme that comes in with the game, but notably, when it asks you to copy a folder, you want to copy the contents (shift select) of the folder that contains the executable of the game comes in (UFO Defense.exe).
Furthermore, when openxcom is loaded you'll need to go to the mods section and x-piratez should be in a dropdown menu.
Some initial settings needed for sanity:
A)There should be an option to show movement TU. If you've turned this on, you should see an AI path and a number for
B)Nightvision mode is also scroll lock by default, which is problematic if you have no scroll lock button, so this should be switched to another button.
C) Air fighting speed should be set to the slowest setting. Air fights go fast and are highly lethal. You might want to speed up some movements as well.
that's all I use, maybe there's some other things some people could mention
2. MAJOR MECHANICAL DIFFERENCES FROM XCOM
There's too many to list here, but here's some that will affect you right away. Read all of the bootypedia's initial entries, here's some that are important whether they're described or not.
A) Holding shift lets you sprint. Maybe this was in vanilla and I was just playing wrong all this time. This causes an increased energy drain, but is honestly the default movement speed in practice. Notably, while sprinting, enemies will get the jump on you if the TU difference between you is enough to cause reaction fire when they first see you. So unless you have a specific goal in mind you might want to sprint a few steps and then walk the rest.
B) You generally have superior night vision to citizens, the most common early game enemies. This makes most early game missions considerably easier during night time (with some exceptions).
C) Listed in the bootypedia but worth reiterating: If you're facing an enemy in melee, when they have their turn you will dodge their attacks. If it's ranged attacks, this costs 6 energy (not TUs) and has a chance based on the evasion of your armor. If you do not have enough energy, you will not dodge! Furthermore, I pistols have an increased chance of defeating dodge, could be wrong
D) Your morale drops over time
3. DIFFICULTY
Generally speaking, there is jack sparrow and everything else. If you're playing something not jack sparrow, you will have a good idea of later game difficulty based on your initial missions. However, the highest difficulty also has some wrenches thrown in and additional base defenses.
There's a button for iron man, but you're better off just deleting your save if you lose than pressing it: the game is extremely long and there's no point in having a save wrecked from a bug.
4. CHOOSING STARTING BASE
There's several good starting options, but there's three that stick out to me:
A) Middle of North America: The main advantage of north america is your radar covers basically the whole continent. You won't need to pursues UFOs as much because they'll just turn around and head back inland.
B) Middle of Africa: My favorite, the main advantage here is a bigger landmass and your back is the pacific ocean. The only missions you'll miss in the first month or two are set in new zealand or hawaii. Also, you'd think desert towns wouldn't grow apple trees (important later), but you'd be wrong.
C) Northern tip of india: Main advantage here is it's 100% land and also mostly backed by the pacific ocean.
5. THINGS YOU CAN AND CAN'T SELL: STARTING BASE
If you sell the Tiny Drill or Menacing Hull, you've basically lost the game. You will get a warning in a research but probably after you've sold it. That's kind of a trend to the mod. So here's things you can or can't sell in your starting base.
A) The Security Corridor: SELLABLE. It says it stops enemies from going in the sewers. It does not. Sell this P.O.S. Or better, build a burrow on top of it (which autsells it and subtracts time from the new building)
2) THE OLD EARTH LAB: NOT SELLABLE. It's like selling your starting lab in XCOM only you can't build any further ones. I'm curious if anyone's played a game where they sell if after reaching mess halls and uber farming and builds a ton of bases, but it's probably not a good idea.
3) ARMORED VAULTS: KINDA SELLABLE: It's a really really nice building. But it's also worth 300k. I sell it, but most do not I think.
4) HI-RES RADAR: NOT SELLABLE (in january). In january you get a bunch of UFOs that land so there is no point. This stops until april mostly, so if you are desperate you can sell it in february (but you're just going to end up rebuilding it)
5) ANY OTHER BUILDING: You can sell them but there's nothing to gain really.
6) TINY DRILL + MENACING HULL: NOT SELLABLE. Just don't.
7) PILES OF JUNK: MOSTLY SELLABLE. These used to be worth more as loot than processing. Now they're worth a fair amount more, but the tech needed is kind of a ways off. There's certainly no harm in selling some or all of it if you feel the need
HELLERIUM + SCRAP: SELLABLE. But the scrap isn't worth much.
9) EVERY OTHER ITEM: Not worth enough to sell or is useful in some way.