Sicilians are actually by far my favourite faction that I've played so far. They're tons of fun I find and the reasons are fourfold.
1) Very low defense requirements. No one can really hit you early on.
2) Massively rich, mostly by trading from Sicily and/or Naples.
3) Tons of opening time due to #1.
4) Tremendously flexible.
Here's my Sicily opening on Hard, GA.
In the opening turn, build a watch tower in each province and move an opening barque into the Maltese channel. On turn two, leave a hundred men in Malta and move your king and the mismatched spears to Sicily and leave a hundred peasants. With a decent governor, the combination of the garrison and the tower will crest Malta just above 100% on Very High. There is no need even to build a border fort though by all means, build one, it's only 200 florins and as we'll discover, you have tons of time and tons of money. Thereafter, if you have autoset taxes on (usually command line my taxes to 105% or 110% loyalty) there's no need to worry about Malta besides to keep buildings in the queue. I'd build towards a shipwright, sneaking 20% and 40% farms in along the way.
Assuming you start in Early, no one but the Italians stand a chance of hitting you early, and they almost certainly won't, unless things go really wrong for the Germans (which presumeably lowers Italian defence requirements enough for them to contemplate hitting you). The Byzantines are extremely weak in Naples and the province actually stands a reasonable chance of going rebel near the start. At Hard and above, the UM that spawn will overwhelm the small garrison there. If that happens, that's a great boon since you can nail it without getting into conflict with Constantinople's fleet. If not, that's fine, you don't need to rush it and if you want to rush it you can do it easily. The Byz will take ages before building a fort there. Or a port. And longer to get their shipping lanes out that far. Likewise, Malta will be untouchable for a while to everyone, including yourself since your opening boats won't be there long.
In fact, I've found in the majority of games, the Sicilian player is not obligated to build anything except tons and tons of boats and tons and tons of economic upgrades out of Sicily for like two decades. Go ahead and throw the florins for 80% farms. The earlier you do it, the more it earns you in the long run. If you arrange the boats and get a trading post started turn 2 (after the tower), you can get trading money from the ports near Genoa flowing into your coffers by turn 4. If you're fortunate enough to start with an acumen 3 or 4 guy, you can be generating thousands from Sicily alone. Just build nothing but ships and take every advantage of the Sicilians' ability to totally skimp on defense in the first decades. I usually aim to get the Ligurean Sea, then around to the Adriatic as both these areas have lots of ports. Best of all, often only the one in Naples will be Byzantine, in case you know, Naples doesn't go rebel and you have to take it the hard way by the time the GA points from it start mattering. After that, I usually get a ship back into the Malta Channel, then down to the coast of Tunisia, (which will soon become important.)
Early on, all you need is enough troops around to discourage the Byz from hitting you. In most cases, you'll soon be up to 61 or more royal knights on top of your 200 spears: far more than enough and it will be a while before the Byzantines are building anything in Naples. Which means initially, you don't need to build a ground army at all. If you do need defence, I don't know why you'd bother with spears. Even if the Byz start kicking ass, they have far better places to send their horse to and it's not like spearmen stand a chance in hell of stopping kitties. I imagine UM would serve you better against Byzfantry but again, this will almost certainly not be necessary until you feel like taking Naples, which you can do anytime before the Byzantines get strong there. Once you grab Naples, the only land border you have is the Pope, who has very little aggression.
The one other thing you do need is naval superiority. First against the Byzantines in the central med and later (duh) against everyone everywhere. In most cases, arranging your opening barques near Naples will be enough as they hold up very well against galleys in my experience. (And you don't care if they're in the area, just so long as you are too, to prevent them from reinforcing Naples). I don't enjoy going to war with the Byzantines though, since it potentially screws up later possibilities, the major one of which is shipping into the Black Sea to grab Khazar. I love Khazar.
Sicily's job is really to make money and you can make a lot of money off Sicily so long as you stay at peace with the Italians. One thing to exploit is that the Italians tend to build most of the ports in the opening turns. Since you're selling to each port, this is very good for you, so long as you remain at peace with the Doge. Sicily's position makes it perfect for generating money off those early ports in the central med. Malta on the other hand, with fewer economic upgrades to worry about, should just hit 80% farming, and then start building towards knights. Not that you can build Hospital knights, but you can always use knights, and they being the most complex of units to tech up to, starting early will help. By contrast, Sicily and Naples build simpler units - Sarges, Arrows, MAA.
Unless things go wrong, the Sicilian king will find his coffers full as Sicily becomes the richest province in the world, and his options limitless if he's playing GA. Sicily gets tons of points just for homelands which initially are just Sicily itself, and Malta. After some turns of generating tons of cash off Sicily with minimal military upkeep to worry about, you can do any number of things so long as you bear in mind that you A) need Tunisia and Naples and B) need a crusade to Palestine.
A rebel Naples is awesome for Sicily. With proper development, Naples itself is very wealthy. I usually just bribe whoever holds the place to simplify things. If it does involve war with the Byzantines, I'd try suing for peace immediately. If denied, I'd sink the Byzantine fleet, invade Constaninople, and hold it down profitably and THEN try to sue for peace again and again. Either way, Naples IMO, should be the first target.
You also need Tunisia and I find the early 12th century a perfect time to do it. Spain and Almohad have generally had time to beat the crap out of each other by then and the Tunisia garrison is often skimpy. Just sweep in from the sea and wash up at Morocco. Morocco, Algeria and Tunisia are fairly wealthy provinces and easy to defend. If built up, Sicily will be the richest guys in Europe, holding just these six provinces.
When that's done, all you need to do to get ahead in points is the highly valuable Palestine crusade. So go ahead, raise an army - and you can afford a lavishly equipped one now - and teleport it over to palestine on your rowboats.
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