on playing the map--
dont open borders. not unless your ready for war. AI uses open bordes for 2 things. settling your lands and scouting your army. use spies to observe enemy army, OB when 2 criteria arre met.
1. AI wont settle/war you. normally they are far away.
2. you found enough rivals to know the diplo scene. then OB with your future-diplo triangle. the less OBs you have, the less (stop trading with civX) you will see.
ALWAYS scout around you, there is bound to be a good city or 2 somewhere. and when you get a resource tech (animal husbandry, bronze working), examine again to see if a horse or copper popped up somewhere.
on REX--
when REX (rapid expand) dont worry about your slider. worry how many BEAKERS. once libraries and courthouses and cottages are running, you will be much happier. 500 beakers at 40% slider with 8 cities is BETTER than 500 beakers on 100% slider with 3 cities.
edit-- too many plantation-requirement resources and no calender any time soon? dont be afraid to farm/cottage them or at least chop the forest on them to make plantation come down faster. milking a tile for what you can get NOW and changing to plantation LATER is a good thing to do.