UnforcedError
Settler
I didn't buy Civ Vanilla as soon as it came out as you did (the reason being Civ 3 which sadly never lived up to my MoO-based expectations). As far as I remember I bought the Vanilla version some 5 years ago finally deciding to give it a go. However, I've been playing strategy games for over 30 years now and being a real geek and fond of numbers I actually started experimenting with various openings for various starts right from the beginning. So I played the game relying on my empiric observations most of the time, which turned out to be wanting as soon as I tried out Emperor. Then I found this forum and read the whole of the War Academy, most of the strategy articles, read game write-ups, watched as many videos as I could, and experimented with the strategies I found here. All these tips and tactics made Emperor a cakewalk and Immortal quite comfortable. I'm just the type of person who doesn't sign up to a forum as long as she thinks she has nothing meaningful to ask / say.Out of curiousity when did you even start playing this game, seeing that you only just signed up this month?
If this game didn't have the concept of tile improvements or even if the difference between improved and unimproved resource tiles was smaller, a city's general progress (growth / resource and commerce potential) would be closer to linear. However, in civ 4 it's rather quadratic or even cubic in the early game (as long as the city can grow onto improved tiles). So 1 city working improved tiles makes much better progress than 2 cities working unimproved tiles, and will therefore be capable of producing more within the same time frame (this is why worker first is generally a good idea).Spain just happens to be a very good Civ for teching an early religion because they can go workboat first. Similarly to Justinian with a Settler first.
Fishing starts, as I mentioned earlier, are generally slower than Grain / Deer / Sheep / Pig starts. The math behind it is pretty simple, while normally a city would build units / workers / settlers in the very early game while workers could improve tiles parallel to it, in case of a seafood start your city has to build tile improvements plus anything else it would normally build. With Fishing / Mining you can minimize the difference by going BW first, but this would still eat up some of your finite (forest) or limited (pop) resources, which you could also find other uses for. And Izzy doesn't even start with Mining. Going for Poly certainly doesn't help, because it does you no good at that stage of the game. If you can grind out a game on Immortal with this tactic, good for you.
Same goes for founding all religions by handpicking opponents and a cooked start: if this was for role-playing purposes and not actually stated to be a winning strategy in the game, fine. I just think the OP actually wanted to read about more general tactics than that.