I thought i might give a water map a try and do something entirely different and go for the warmongerer route this time. The question is how excatly do you approach a watery map as an aggressor? I have limited experience on waging war even on pangea and i guess the archipelago might need some more unorthodox strategies or ones which deviate from the ones that ppl usually use on land.
Good shout! This is exactly what I am doing atm too. What difficulty are you playing on? Standard map, standard # of civs. Playing as England on Emperor with only Domination victory on. How do you approach this kind of map? For me it's about settling your island (I managed two cities), exploring ASAP, settling colonies on good city sites, keeping ahead in tech (most important) and having a strong navy.
1)What should my tech path look like and which units to emphasize?
Aim for Sailing early - you need to get exploring much earlier than on, say, Continents. Don't worry too much about decent land units. The top half of the tech tree is key. Whilst exploring, go for Ed
For defence, emphasize a ranged land unit for defence in each city. Ranged ships are also perfect but I find that these get called to the front later.
For offence, you seldom need land units (unless the city is not on the coast or only has one water tile next to it) so concentrate on 4-6 frigates and 3-4 privateers per city. Prior to Navigation capturing a coastal city is doable but tough. Late game is where Archipelago maps come into their own with the range of units. Just remember the rock-paper-scissors mechanic and that you'll need 4-6 ranged naval units and 3-4 melee naval units per city.
2)Policies?(I was thinking a combination of liberty+honor might do the trick, with some commerce later)?
Liberty/Tradition first depending on preference. I would go Liberty as you will be going wide through domination. After finishing Liberty/Tradition I would recommend Commerce if it's available. Failing that, open up Honor.
3)Sea-land unit ratio?
A very rough ratio would be 4:1. One ranged unit per city and perhaps a naval unit or two sailing around your cities for defence. 4-6 ranged naval units and 3-4 melee naval units per city for offence. You will seldom need more than one land unit per city. The only exception would be if enemy cities (or your own) are in land, which is rare (especially for capitals).
4)Wonders(Great Lighthouse maybe, ND later i guess)?
Personally I aim for the Great Lighthouse but on Emperor+ there is no guarantee that you will get it. Commerce has similar benefits.
5)How many core cities do you usually go for?
I settle as many as possible on my starting island (I've never managed more than four cities and that would arguably be an ideal maximum to start with until NC). After NC I settle on strategic islands and resources. This can prove tough to defend and pisses off the AI so be warned!
6)Who to actually attack first(nearest neigbours, the one with luxuries/resources or the weakest civs)?
If you have a neighbour that is so near that they are in the way then go for them. I usually aim for that kind of neighbour first and then go for the top two civs (by that I mean the runaways who have all the wonders, 10 cities, are close to leading in tech and have spammed units). It may sound ridiculous to target the hardest civs first but once they have been conquered you have nothing to worry about. After all, you wouldn't want them to become an even bigger runaway whilst concentrating on less powerful civs...
7)How to keep up in tech, since nobody will DoF with an aggressor?
A few civs will (hopefully) remain friends. I've managed 3 out of 7. The other 4 are in a permanent war. I wouldn't rely too much on RAs though as the AI will often backstab you on Domination+Archipelago. How to keep up in tech then? Universities is the answer - build them in your core cities and staff them! Currently, I've got two fully staffed universities with 11 cities (my other cities are too small or are defending against the AI to staff/build universities) and I am leading in tech in the late medieval era. Settling a few GSs early can help no end.
One final note - you may find it hard to make allies with the AI and city states because you will be seen as an aggressor. Don't dispair. The most important thing is to keep ahead in tech otherwise you will struggle to tackle the larger civs. It is likely that your game will go on into the 2000s. Personally, I like it that way as late-game naval warfare is great fun! Just make sure you have conquered a few of the AIs capitals before then!
Good luck and keep us posted on how you do.