You can change the amount of turns in the standard game preferences before you start. In the same window that controls how many cities are required for Elimination, for example, or how much gold a Princess will give you (even though Princesses are pretty bugged as far as I know)
Well well well. I did not know that, and now I have learned something new about this great game. Thank-you (both) very much.
I am not sure what a .biq is. The game did appear in my Hall of Fame, so maybe I did leave it unchanged.
The .biq is the ruleset file that the conquest .exe uses to create a (new) game. Data from the .biq (including the map, whether randomly generated or preset) is then stored in every .sav file for that game.
It includes the tech tree, tech-costs, terrain yields, units/buildings available, unit/building statistics, etc., and it tells the game where to find all the needed assets (animation-files, sounds, etc.) if anything new has been added. You can edit the Conquests .biq using the included Editor (even adding completely new units, so long as you have the files to go with them), but as I say, if you do (and over-write the original), then you will no longer be playing the 'epic game' so scores are not recorded (because they would not be comparable).
However, anything that can be changed in the game setup screen does not affect the .biq itself -- so your score is still recorded.
My civ4 game regularly changes the assets mid-game and wrecks my plays
Civ3 does do that from time to time: strategic resources, once hooked up to a trade-net, may become randomly 'exhausted'. But this actually just means that they disappear from one tile, and re-appear somewhere else instead (this possibility, and the frequency with which it happens is also set in the .biq!)
I did change the amount of turns in the length of the game to the maximum value, which is 1000.
See above. I've been playing Civ3 since 2009 and Conquests since 2012ish, and I did not realise this was possible
I believe I also disabled "culturally linked starts" and wonder victory, because I didn't really understand it and the description that I read sounded like it didn't really add anything to the game.
If you habitually Randomise your own Civ (as I do), you should always turn off Culture-linkage, because it's bugged. If it's turned on, then you'll always get the American Civs on the board -- which means that on a Standard map, 5/8 Civs will be American, and 4/5 of these are Agricultural (the strongest Civ-trait in Conquests, which really helps the AI out).
The Wonder VC is more intended for Scenarios (e.g. the Mesopotamia-Conquest uses it). What it does is force an 'early' end to what might otherwise by a straight Histographic game (2050 AD, if you haven't changed the number of turns to win!) -- but you need to have the highest score when the last Wonder gets built (by anyone), or it's a guaranteed defeat.
Can I ask about your thoughts on increasing to monarch?
Monarch? Naaah... You've just finished showing us that you're already competent at Regent, so you've got a pretty good handle on the game: if you want to increase the challenge, I'd suggest to just skip straight up to Emperor. Yes, really!
The main/only noticeable difference between Regent and Monarch is that at Monarch, your people start getting unhappy sooner (only the first citizen per town is born content, instead of the first two citizens), which makes the early game a little more challenging (you need to use the LUX%-slider a little more). The Monarch-AI does also get an extra Worker and an extra defender(s?) to start, and a 10% discount on growth, build costs and (compared to you) tech-beakers, but it continues to be pretty inept at tile-improvement, micromanagement, and warring (and it still won't build Artillery!), so the early game still feels pretty much like Regent.
And the only additional (noticeable) differences between Monarch and Emperor are that the AI's discount goes up to 20%, which makes up for some of its ineptitude/wastefulness in early production/growth (brings it to pretty much an even standing with the human), and it gets a few more starting units (3 defensive, 1 attacker, 1 more extra Worker, IIRC). So you need to pick your priority town-sites carefully, and you can't faff around quite so much with buildings, you'll need to put more early shields into units (including Settlers and Workers).
But if you're still doubtful, just pick the Mayans as your Civ (IND + AGRI = strongest Civ in the game, usually!)