I've never built any customs houses, so I'll try that.
When I got complaints from colonies that I was supplying them with an "untrained" colonist, I took that as an insult, so then I sent these colonists to found another colony, but later on found I could force these colonies to accept them anyway, so I did.
I have never had anyone trained in Europe either, because I usually couldn't afford it.
Find a good place for your first colony with a lot of food and some other valuable resource. Dont built it just anywhere. Build town defense (stock gate etc.) as fast as you can. Use artillery just for defense and and keep them fortified. Plan your other colonies also on good places, no need to be on the ocean, you can use wagon trains for transport.
For attack use dragons, if you win a few times they will become veterans if not already.
Also you can trade with indians also and they can train your colonists. Use the extensive information in the game about units and terrain and it will get you much further in the game.
Also for me its better to accept the tax raise every time until you have enough liberty bells to declare independence.
