might not hurt to periodically reread paul's page,
http://members.home.nl/paulvdb/occ.htm
1) sometimes customizing of the world will help. There have been a couple threads here that discuss that (somewhere in the stratagy forum anyway - did you reset it so you view all topics instead of just hte last 10 days?)
2) Romans and other white civs get first random picks, so yes, but you already are choosing white
3) According to Paul, sea is neutral (and above desert/mountain etc). You'll see that whales are considered one of the best specials in any case. They provide good trade and eventially decent food and production.
4) Alliances can chop centuries off your landing dates, although it sounds like you are managing reasonably well giftwise without them. In terms of city building, if you have an alliance, their units can't take away control of your land if you are already working a particular tile.
5) only grasslands can hide specials, since only grasslands don't have a special terrain type.
6) you probably have a better grasp of how to trade techs than i do - i keep accepting trades early on and it takes me millinia to get to monarchy

I have yet to figure out when to stop gifting, and while i stop earlier than you do for the most part, I generally have to research several techs (feudalism/chivalry etc) that others can trade for. Most people will avoid gifting combustion until they have discovered flight to keep the colossus in effect.
have you tried any of the comparison games or fortnight games yet? playing them and then reading others' logs afterwards can often show why people do certain things, if not why they discovered certain things in a particular order.