Hi Federro:
wow, a lot of questions:
With JForex strategies you can access your external jar files with the annotation "@Library("path_your_lib1;path_your_lib2;and_so_on"). Wiki example
here.
Also you can do inner classe objects inside your strategy file. One example of that can be this strategy from other user with external jar and modified by me to not need the external jar
here. Here with both examples (the original strategy and my modifications) you can see examples for both of your questions.
Trade well and good luck
JL