Hi guys, thank you for taking the time to read my thread, Civ 5 was my first Civ game and I loved it! It was super enjoyable but got a little stale after I logged hundreds of hours into it. I decided to buy Civ 4 last night and I have some questions I hope someone can answer for me =P
1) I understand the concept of slavery and I use it whenever the option appears, but when is the wisest time to stop slavery? And what does "whip production" mean? Can I stop it when my city is healthy? What are the repercussions?
There is something like a rule, that "a 1

3

tile is about as productive as the whip" , so that means, you can whip away everything that's worse, and only grow onto those tiles while you wait to get a military key unit.
Ofc. this rule (despite being very good) is wrong, because to really get an answer, you need to evaluate every whip in single, then simply divert the

you get from the whip through the number of

needed to regrow, then you'll know the value of 1

. Should be something between 1 and 2

.
Letting cities grow bigger instead of whipping them continously is something for games where you want maximum research (i. e. a Space Race) , because bigger cities ofc. can produce more research, due to their better Traderoutes mainly, and ofc., additional tiles may also yield

. If you play for Domination or Conquest, no city apart from your capital, which always should be as big as affordable, needs to grow larger than size 8 (size for 4-pop-whip) , often 6 or even 4 is enough though (sizes for 3- and 2-pop-whips) . Your capital shouldn't be whipped at all past a certain point early in the game, because if you specialize your capital to

, found an Academy and run Burocracy, your capital makes the greatest part of your empire's

.
2) In Civ V, founding new cities means less happiness...what are the repercussions of founding new cities in Civ IV?
Happiness depends mainly on the resources you have, and partly on some buildings giving Happiness. There is a very good guide on it, called "Ways into Happiness". You can find it in the Strategy Guides subsection.
3) Why do the other nations' scouts and warriors keep going back and forth on my land after open borders? I read somewhere that it is best to always agree with other civs demands...when is it wise NOT to?
1. There are begs and demands. Begs are, when the civs is above the threshold where it can declare war on you, demands are where they actually can declare war at you. You'll get negative diplo for denying both types, but only the 2nd type is dangerous, because then, a civ can jump instantly into war-preparation-mode and DoW you 10-20T later.
2. You only need to agree with demands if you fear war or need positive diplo. It's very wise to get a few civs on friendly, so that they're willing too trade even monopoly techs, this can be quite easy if having agreed to one of their demands and quite difficult if having negative diplo from having denied one. Be careful with demands to join their wars though, those come frequently, and when you're not ready, you must not agree to them, except if the war is with a target that can't reach you because it's far away, then you only need to be aware of getting -1 or -2 with the friends of the target, but better have some friends and foes than none of both.
3. Don't hand out military key techs, unless you know exactly what you're doing. You don't want someone to become strong, unless he's your ally and you have nothing to fear from him and also don't plan on invading him nevertheless.
Open Borders are neither demand nor beg btw., they're just a normal trade from both sides, and you should always agree with them, unless someone who is the worst enemy of several others asks you, because you cannot have Traderoutes without open Borders (except for very late when the UN is available) .
4) How much military should i have? And what are the repercussions of having too many?
You should have as little military as needed, so keep peace via diplo, and only guard cities that would suffer from too much

if unguarded with a Warrior or Archer.
Then once you got your desired military key-tech, whip / draft out as many units as needed to conquer your opponent or also as possible if playing for Domination / Conquest.
Every unit above a certain limit costs you 1

, so don't build unnecessary military. Also don't have your troops standing around, except for the City Garrisons I talked of. Expensive units must conquer, otherwise, they're a waste of resources. If you get DoWed unexpectedly, whip a Walls in the city that gets attacked, this forces the AI to bombard the defenses down, which gives you enough time for reinforcements to arrive. Even if he attacks directly (because he has no units for bombardement) , retaking the city is better than to have spent xy(z) amounts on unnecessary unit maintenance.
Thank you for all your help!
You're welcome

.