To answer your question, they serve completely different roles on a battlefield.

Swordsmen = Flank
Hoplites = Front line

You need enough Hoplites to cover your front line so that you can fight the enemy, while your swordsmen (your flank) take out the enemies long range units, and then attack the enemies front line from the rear (assuming they do not have swordsmen too).

They aren't competition for each other because if I sent an army of fully upgraded swordsmen to fight an army of fully upgraded Hoplites, the Hoplites would destroy the swords. Swords are not meant for front line, and you'd do better to use them in the flank where they shine before anything else.

Like Nikolai said, Hoplites are stronger than swordsmen man per man and in a fight of all hoplites vs all swordsmen, the swordsmen would lose BUT in a real combat, that's not really the case. That's where the flank and frontline (which Nikolai also mentioned) come into play.

If go to Help-The Art of War, it actually gives you a pretty good starting point to base your basic Ikariam warfare knowledge as the mechanics are well-explained. (No strategies are explained so don't go thinking you're a master if you read it, but it gets the mechanics.) One thing you'll read it about are the different lines of combat. Hoplites go on the frontline while swordsmen go on the flanks. They perform different functions because of that and you do need both win so in all honesty, comparing swordsmen and hoplites is like comparing apples and oranges. The true unit to compare swordsmen to is the spearman, which the swordsman beats.

That's the TL;DR portion. The following is me rambling to completeness.

In the battlefield on land you have a total of six lines. The first is the bombers which is filled with bombers. They're primarily to attack enemy artillery. To counter the bombers, there's the air defense line (by the way, these first two names may be inaccurate as I'm doing it by memory) made of gyrocopters which attacks bombers primarily. The artillery line, made up of rams, catapults, and mortars, primarily attacks the frontline. The longrange line, made of slingers, archers, and guns, primarily attacks the frontline too. The Flanks made of spearmen and swordsmen, attacks the flanks first. If there aren't any flanks it attacks the longrange, then the artillery, then the frontline. So if you don't have flanks, your guns (most likely) which are precious, get killed. The Frontline made of hoplites and steam giants [SGs] has to endure the assault of the artillery and longrange and then attack the opposing frontline. This is also the line that grabs everything to fill it. If there aren't any hops and SGs left, it grabs from the flanks, and then from longrange units out of ammo. (You want it to only have frontline units because other stuff sucks on the frontline.) If the opposing frontline goes, it then attacks the longrange, then the artillery, and then the flanks.

Kaleg and Nikolai pretty much answered most of what you asked but the 3 and 5 values on Swordsmen and Hoplites respectfully are not carry or loot values but rather how much space they take up on Trade Ships while traveling from island to island. Only Trade Ships can carry loot and only Trade Ships can carry troops(hence if you pillage a town by sea, your Trade Ships have to carry the surviving units back home, which cuts into how much loot your ships can take back).

Assuming you have enough frontline troops to maintain the frontline, then yes. They fill the field automatically. The only manual part of battle you do is sending in and recalling waves.

What Kaleg said. As long as you have enough soldiers to fill each space for Front line, Flank, Artillery,and Air (Gyro's/Bombers) you should be good.

If you have trouble finding out how to fill out spaces for different sized colonies then you can always use http://ikariam.wikia.com/wiki/Main_Page to search up the units and how many of each unit you will need to fill the battlefield + more.

It may be outdated, but I still use the Wikipedia and some older Ikariam threads to decide what I build my armies with. It usually depends on if they are an active or inactive player that I'm pillaging too.

On another note: You can always consider waving;really complex,time consuming strategy, after you research Steam Giants. I haven't fully grasped the Idea of waving but when fighting larger opponents and to reduce casualties, it is best to attack their town with Hoplites first as fodder against their wall, while sending in a fresh batch of soldiers (giants, hops, swords,sulfur carbs) when the wall is down and you are fighting their soldiers. It's time consuming and you have to watch for different army morale/landing times for armies, but it usually pays off in things such as a war.

I'm sure more experienced players here can give you more details into waving if you have any questions on it.

You're correct with the resources. Gold pillaging only happens against the barbarians however. You cannot pillage another player's gold.