I can not stress enough how important this decision is... there will be HUGE differences in the game, depending on what setting is chosen...
With tech trading ON, forming and maintaining tech trading alliances will be a critical part of the game... So diplomacy will be very important.
If tech trading is ON, we will have lots and lots of diplomacy-related talk, mostly revolving around making and managing tech alliances, and one time tech trades. We will always be talking about diplomacy, and meeting our rivals before the other teams do will be one of the most important things in the game.
With tech trading OFF, mastery of tile, city, and specialist micromanagement will be essential, because it will be those small advantages... an extra beaker here, an extra commerce point there... who gets a great person first and what type etc., which will allow one team to get ahead in tech, growth, everything.
If tech trading is OFF, the discussions about what we will do each turn will be dominated by MMing (micromanagement) talk. For example... Whether to work the corn or the gold and how many
versus how much
we will generate by doing one or the other. We will talk about this stuff anyway, but with tech trading off, it will be a much more important part of our game.
Restrictions on tech trading tends to favor players with tons and tons of MP experience, because those are how ladder games are typically played. I can say from experience, that most casual players do not think alot about MMing, and you will learn alot of new stuff about it just by participating in this game. MMing is a little more technical and requires a little more research and calculation than diplomacy, because it is all about the numbers.
Diplomacy (diplo) on the other hand is a little bit less about CIV and more about people, politics and interpersonal relationships. The skills needed for good diplo are different from the skills needed for good MMing, but generally, it takes more CIV experience to be good at MMing than it does to be good at diplo.
I hope this was helpful.