Everything [to_xp]Gekko said is valid, but I'll throw in some additions:
1)
(edit: I found version "i", thx (you guys should replace the main file download with a patched one...))
Patches are released more or less frequently. They are seperate from the main download so that only the changes will have to be downloaded each time a change is made, rather than every FfH2 player having to redownload the entire mod each time. The bandwidth savings is considerable, and everyone benefits - except for a first-time player, who must download the main mod and the patch anyway. If that player continues to play, and applies new patches as released, the initial inconvenience will pay off in the long term.
2) Pirate Coves give +2

, but no extra

or

. They upgrade over time to Pirate Harbors, which give +1

/ +1

/ +3

, and then eventually to Pirate Ports, which give +2

/ +2

/ +4

.
3) If you play a leader with the Arcane trait then your Arcane units will earn free xp at a faster rate.
6) The Guardsman promotion will prevent enemy units with the Marksman promotion (such as Assassins) from being able to target the weakest unit in the stack. The Bannor civ has the advantage that several of their unit types start with Guardsman for free; everyone else must earn a purchase the promotion, which requires Combat IV as a prerequisite.
Alternatively, you can kill their Assassins before they kill you, by attacking first. This is less reliable, however, because enemy Assassins are not alway within reach.
7) One or more Water mana will allow you to purchase Water magic for your Arcane casters. If you have two or more Water mana then your new Adepts will start with Water I for free, and if you upgrade an Arcane unit to a Mage or Archmage then it will receive Water I for free. If you have three or more Water mana then any Arcane units you upgrade to Mage or Archmage will also receive Water II for free. If you have four or more Water mana then any Arcane units you upgrade to Archmage will also receive Water III for free.
If you buy promotions and then later qualify for those promotions for free they are not refunded. Whether this is a wasted promotion is a matter of perspective; yes, it does mean that potentially your Mage could have spent that promotion on something else, but in order to get Water II for free your Mage would have had to remain an Adept until you got access to that 3rd Water mana. If your Mage got any use out of Water II (or any other second-level magic) during that time when you didn't have three Water mana then I wouldn't call it a waste.
8) This is a very complicated topic, and different players will give different answers. Your situation in-game will make some spells more useful and some less, so that you will want to choose your mana accordingly. Fire II, Sun II, Enchantment I & II, and Entropy I are almost always useful. Also, all of the summoning spells tend to be useful because having disposable troops to soften up enemies is handy. My suggestion is that you try out all the spells for yourself, and then make up your own mind about which ones you like. This has the added benefit that if you find yourself in a situation where a normally less useful spell is actually useful you will be able to think of trying it.
Also, with regard to the small number of nodes available, you should be aware that Metamagic II allows a node to be dispelled - which turns it back into a raw node. It can then be made into a different type of node. Once an Arcane unit has purchased level I of a type of magic (Water I for example), it will be able to purchase levels II (if a Mage) and III (if an Archmage) even if you no longer have access to that mana type. You can give your casters access to many different types of mana even with only a few available nodes if you use Metamagic to change the nodes around. Just remember to save one raw node until you research Sorcery (required to make Metamagic nodes), or you'll have to go find a new raw node before you can learn Metamagic spells.
9) Getting enough Great Prophets to complete the Altar of the Luonnotar isn't too hard, if you plan it correctly. Avoid non-priest specialists and wonders that give

points for anything other than Great Prophets. Use civics that boost your

production rate (Pacifism, Republic, Arete) or allow more Priest slots (Theocracy). Naturally, Philosophical leaders will have an easier time thanks to their increased

rate. The last stage of the Altar must be built, and requires a very expensive late-game tech, so you have plenty of time to get the 6 Great Prophets you need.
10) This topic spawns many debates among FfH2 players. I'll tell you my opinion, but you should take it with a grain of salt and form your own opinion as you continue to play.
My first 9 techs would be: Agriculture> Calendar> Crafting> Mining> Ancient Chants> Education> Animal Husbandry> Festivals> Exploration. The 10th would be either Mysticism, Cartography, or Code of Laws, depending on which government civic I was planning to adopt. Naturally, in a real game, you would need to adjust this order to suit your starting area and the resources in it.
My first 10 builds would be: Worker, Scout, Warrior, Warrior, Warrior, Warrior, Settler, Warrior, Warrior, Settler. Worker-first is controvertial and dangerous. Here I assume that you pull back one of your starting units to defend. If you explore with both your starting units then you are probably better off building a Warrior and then a Worker. Also, if your initial explorers die early then you should probably replace them with Scouts. Early scouting is important and shouldn't be neglected. The difficulty level you play on, and your barbarian settings, will have a big impact on the build order you should use.