I will remember about "food in first ring" rule. I've never heard about it before and haven't "invented" it by myself.
Yes, in the early game food resources are the most important resources. A city must grow a bit to become productive. If you for example settle next to gold, you can't really work that gold mine until you've grown at least to pop 2, or growth stagnates. Also, with slavery food yield is worth a lot more hammers than actual hammer yield while your cities are small. With good food a city can grow quickly, whip in the essential infra and grow back quickly for more whipping.
Few questions:
1) Should i build cottage on plains? If not, then cottage only on grasslands and floodplains?
Plains are bad tiles because they are food negative (each population eats 2 food, plain tiles give you only 1 food). As mentioned, you should avoid them in the early game. You are better of whipping away that population, into for example an army that can go get you some better lands to work.
2) why GLighthouse wonder is so good? yeah, i know, +2 trade routes, but really it is so important? which wonders in the ancient/classical era are usually the best (yeah, i know, it all depends on circumstances, but come on, there are surely some principles); for example, i value the most - by far - The Pyramids; then GLibrary, Parthenon, eventually GWall can be useful; GLighthouse, Colossus, ToA, Stonehenge as a luxury;
If you have currency ant GLH, then each new coastal city automatically gets 4 trade routes. With open borders to your neighbors and enough foreign trade routes, this usually means +8
at least. Later on it can grow to a lot more, especially once you get astro for intercontinental trade routes. You can also settle a few cities on islands to get higher yield offshore trade routes in all your coastal cities. Early on, settling a new city often adds less than 8
to your total maintenance. This means that with GLH the new city immediately upon settling results in a net gain to your economy.
Or if you look at it another way, when you settle coastal cities with immediate 8
in trade route income, it's like every one of them got a free riverside financial gold mine compared to settling a city with no trade routes at all.
3) barbertje found his 2 cities on the north and south quite far from capital/his border; is it good in this "starter"? what about maintenance?
This depends. (Didn't look at barbertje's save.) If you can grab strong commerce tiles, then the generated commerce will overcome the added maintenance quickly for a net gain. Or if you this way can block off your opponent to secure that you get a lot of other good spots later, then it might also be worth it.
4) his city on south was founded on floodplains? is it advisable despite of health penalty?
There is no health penalty from settling on FPs. FPs work like forests, they are an addition to a desert tile that disappear when you settle on it. Then you have your city on a normal desert tile. Usually it is adviced against doing so mainly because floodplains are such strong tiles to work and you don't want to waste them by settling on them. But sometimes, depending on the map, it might be worth doing so anyway. There is a health penalty from floodplains in the BFC, but this is so low that you shouldn't worry about it. Trade actively for more health resources (or take them by force
) and you will be fine.
I say go ahead and aim for immortal!
Once you get the basics right you will shoot up in levels quickly!