What is the easiest start? Is there a leader that is easier to start with or should I go random? Otherwise, looks like pangea, standard map, temperate climate?
I think best start for an absolutely first game would be a small or duel map on settler level - and maybe not an archipelago map. But all the rest does not matter too much, to understand the basic mechanics, so don't worry. The game should provide you three game icons (Civ IV standard/vanilla plus the two expansions Warlords and BTS) - and I would recommend to frist try the Tutorial that comes with the standard game. I would recommend to start with the standard game anyway, as especially BTS comes with a huge load of added stuff and game mechanics that might be very confusing and over the top for an absolute beginner.
Btw. the game has a built in world builder that can be accessed anytime directly. So you can use this game more or less like a physical board game and can change whatever you want whenever you want - if you don't check it off deliberately. With this you can cheat, tinker and experiment with the game situation as much as you want. There's no need to be afraid of making mistakes.
Enjoy!