Too lazy, miss candy?
Ok, let me give my 2 eurocents of knowledge:
Starting in isolation has his pros and cons... You had putted on the table a lot of the cons: AI trade with each other, have foreign routes.... But there are pros: Ai don't hate you as much as in a normal map ( they will dislike more their neighbours than you ), you have a certain margin of manouvering about the military until someone gots astro ( or Optics, if you have João in the game

) and you have a island all by yourself, letting you to choose the best spots unpressured by some land grabbing AI
You said that you have less tech power than the overseas civs.... that is a normal thing ( I'm used to have a 8 - 10 techs handicap at the time of first contact ), but remember that you don't really need all of the techs and that some are far more important than others. The key is to focus on the important stuff
Some things that you should do:
-Check that you're really isolated as soon as possible.
-Avoid early wonders ( this has some exceptions, depending of your game style, leader and civ: I like to try the GW or the Henge or the Oracle ( I doubt that you can gat them all ) and focus on settling good spots
-Focus on economical techs: CoL, Currency, CS, Calendar ( if you have the resources ) and Monarchy ( this one is not so clear, but having Hereditary rule allows you to have some really nice cities ( 8- 12 pop ) in the beggining of the AD era. More worked tiles = more everything )
-Unlike Gooblah, I do not advice you to pursue Optics: it requires Machinery and compass, 2 techs that won't help your economy much in isolation. IMHO those beakers are more well spent in Philo or in the Drama side of the tech tree. Let them find you....
-Focus on getting Education ( more

and in path of Liberalism ) and Lib: this is a good tech to have in isolation, not only because of the free tech, but also because of the Free religion ( if you don't have the S. Paya ). AI like to stick to their religions and if you can pass somehow unnoticed, the better. But just in case get a sizable stack of cats and of the best units you can get,just in case....
I believe that the key of coping isolation is to be prepared for the inevitable day that you will contact the AI. Yo should focus on having a strong economical infrastructure ready in that moment, because if can do that, even with the heavy tech and military handicap you'll have, you'll be able to get parity with them in no time and skyrocket in front of them. After that any win type ( even cultural sushi powered one or space ( i like to pursue space in isolation: it requres a nice tech research plan and nerves of steel ) ) is easy.