I am also a good old fan of RoN. Bought the game when it first came out. It is such a great game into which I invest quite a great deal of time and effort. Initially, I searched for forums to read about. I hit Heavengames.com and have settled in here since then.
At the beginning when all of us were pretty much the same as far as our skill level goes; we investigate many aspects and properties of the game. There were many many many threads which lists out figures, numbers and even methodology ansering questions of the sort.
About farms, which means food, there are quite a few famous theories stated by experienced players, now they should be veterans. If my memory serves me correctly, you do not build more than 10 farms in your entire life span. That is to say, you only build farms in 2 major cities which obviously are the capital and the 2nd city. They made some calculations which prove that being accurate. For Japanese, you need even fewer farmers. There is also a theory that it is not necessary to build more than 2 granaries, now for that I am not really sure about.
For me, I search for rare resources which boost my food and timber cap to the limit. So I don't normally make granary in recent games. I only make 1 in case I have chosen a nation which is slow in food production or when I need to upgrade fast throughout combats.
To be honest, I never play water maps. I play Great Lakes and African holes or Australian outlook which are members of Random Land Map. The map in RoN in fact needs more varieties. But I would guess that using fishing boats with some escort will be sufficient for generating food. The safest is to cultivate farm even in a water map.
About buildings, I would build temples in each city. Same for University unless the game ends in Enlightenment or Industrial. Becoz knowledge is greatly demanded by research post-Industrial. The more University, the faster you can go Modern and up. I build 2 libraries for simultaneous research. I keep 2 markets, one for back up.
You may be surprised to see my recorded games, when you find my build an empty city. An empty city is for expanding border. It would also be useful for getting an oil well within city's economic radius or make some room for wonder. Another advantage of an empty city is that you can always make some military buildings behind the city so that the city itself is used as a cushion.