Aye... sometimes the AI comes up with some pretty insane trades/demands. However, there are many times when I've come out smelling like roses from a trade (i.e. heavily in my favor). In my mind I've damn near crippled Civs just from my heavy trades -- like a certain Civ paying me +300 gold/turn for a tech, luxuries, etc. The bottom line is this: if the price is too high, don't do it. If it's something you _really_ need... well, that's the name of the game. You're going to have to make sacrifices from time to time.
The AI will only respect your borders if they know you can kick their ass. And by that I mean you have a huge military advantage. Even then they'll still try and move across your territory. If the AI has a huge military advantage over you, they'll come and go as they wish -- and generally I'll let them do it (especially if they're in a position to obliterate me).
The AI, IIRC, only "cheats" at Monarch level and higher.
As for workers: DO NOT AUTOMATE THEM. Well, don't automate them until well into the "late game". Actually, there are times when I have so many workers (from conquest, trades or just outright building them), that I will put a couple of them on automate.
Keeping your people happy: It took me many games to finally realize what was going on here. It comes down to four things: luxuries, luxury tax, garrisons and "happy improvements" (temples, cathedrals, etc). Generally I never have to take my luxury tax up over 0%. And if I do, it's never above 10% for more than a handful of turns. I'm obsessed with obtaining luxuries and/or trading for them. In conjunction with a marketplace, you can keep a lot of folks pleased. Also, if you're running under Despotism, Monarch or Communism, you can use garrisoned troops to keep your people happy.
Tech Race: The AI civs generally get ahead in tech quicker because they trade techs like mad with each other. One word of advice: as soon as you research a new tech, shop it around to the other civs and see what you can get for it. You might as well do it, since they're, most likely, going to get it sooner or later anyway. In some regent level games, the only way I can stay abreast of the tech race is by the heavy trading/purchusing of techs. If you want to just flat-out "win" the tech race (or be the forerunner) you're going to need the infrastructure to support it. Personally I don't creating scientists does jack squat. What helps the most is Libraries, Universities, Research Labs (and lots of them). Don't forget your science boosting great wonders, and a generous helping of funds being spent into your science rate (ideally 60%+).
Just keep playing around with it... you'll figure it out (I did). What might help is if you read the Succession Game forum.
Out,
Volstag