I went from Lanun to Calabim as a swap because as soon as I got to Basium, I'd be screwed because I had no understanding of resourcing on land.
How you play the Lanun or Calabim will be different based on whether you are trying to win the game with that civ, or trying to win the game as the Mercurians after summoning them. Winning as the Mercurians has almost nothing to do with how you develop your tiles. They start allied with your former civ (and so research of your own is unnecessary) and get free Angels when units that follow Order, Empyrean, or Runes of Kilmorph die (and so production is unnecessary). All you have to do is encourage civs that follow one of those religions to get into wars, support your army, and conquer the world. Adopt God King (but switch to City States or Republic once your empire gets large), adopt Military State, build cottages everywhere you can.
As Calabim, I'm clearly an under-achiever. I'm playing on warlord and I can't keep up resource wise with the computers. I build tons of farms, cottages, mines and lumber mills around all my cities, grab every special resource, but I can't seem to get my cities running fast enough, other than maybe my first two. I was using Aristocracy / Agrarianism. I was out-resourced and out-built, and it seemed the only thing I had any small advantage on was tech. I've tried this about 3-4 times now, and I'm always out-done.
Aristocracy + Agrarianism is great, and all you need to do is farm everwhere (sometimes I will cottage plains tiles instead, so as not to lose the

, but for the Calabim this is unnecessary as the Governor's Mannor ensures that your cities will have decent production output even without working any tiles that produce

s) - but you need to get to Aristocracy first. It is easy to fall behind before you get there. Unless you have early access to many high-

tiles you should get to Education quickly and build cottages to help you tech to Aristocracy, otherwise you'll be playing catch-up with your farm

trying to compete with the AI's Villages and Towns.
The AI will always out-produce you. Beating the AI is not about producing more units than them, but rather about using the units you do produce in better ways. As the Calabim you have access to Vampires, which can Feast on your population to gain experience without the risk of combat. Rapid population growth in your cities (thanks to extensive farming + Granary/Smokehouse/Breeding Pit) will allow you to Feast more often, allowing your Vampires to gain experience quickly, making your Vampires much stronger than the units fielded by your opponents. Your army might be smaller than those of your opponents, but it will be much better. The ability of your Vampires to summon units can help make up for any shortfall (Spectre Fear can keep an attacking army at bay, as well as potentially splitting up an attacking stack into more manageable chunks).
Lumbermills are not very good. At higher difficulty levels, where

can be a major limiting factor, they may be necessary, but whenever possible you should be chopping down forests (to speed production of necessary buildings, especially ones with a production bonus when possible) and replacing them with better improvements. If you must save some forests for

reasons, make sure to save ones that are adjacent to (not diagonally) a river so that you get the one

; Lumbermills that are not adjacent to a river are truly abysmal. Frankly, I question the wisdom of even researching
Archery until after you have
Feudalism. Unless you are in a really bad situation you can probably defend just fine with Blood Pets and skipping
Archery will get you to Vampires that much sooner.
Here are three 10-step strategy guides for the Calabim:
Doug Piranha's Calabim Tips
Ekolite's Calabim Tips
readercolin's Calabim Tips
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Also, I like going for an Altar victory, but it seems late game I can't pull great prophets to save my life. I can get the alter to 3-4, but then it's almost impossible to get another one to proc, even with pacifism on. Any suggestions?
Producing lots of Great Prophets is mostly a matter of using Priest specialists and avoiding the pollution of your

pool in cities that are going to be producing Great People. Pick 1-3 cities that will be your

producers, and maximize the number of Priest specialists they can assign (by constructing buildings that provide Priest slots). If you build wonders, then build wonders that offer a

bonus toward a Great Prophet on your Great-Prophet-producing cities and build any wonders that offer other

bonuses in cities other cities. Be sure to spread out non-Great Prophet wonders among your non-Great-Prophet-producing cities, so that no one city will be able to accumulate enough

points to beat out your Great-Prophet-producing cities at some future time. In the later stages, when the time between Great People gets long, consider switching to Theocracy to allow even more Priest specialists to be employed, so as to reduce the production time. Finally, conserve your Great Prophets: if you know that you are going for an Altar victory don't build more than one religious shrine and don't settle your Great Prophets. If you end up with a Great Prophet but don't yet have the tech to build the next stage of the Altar, save the Great Prophet until you can.