How footwork and kicking in JunFan/JKD could be developed to the fine edge? What is better for begginers? to learn perfect form by isolated movements or by dynamic application with a partner and combination kicking to kicking shield? Sorry for my grammar.

Form before function always. If a student cant perform the action properly theres no reason to drill further, or you can create bad habits for him. And seperate drills to supplement footwork is always good practice

Another good waypoint from You, Your experience really helps, I have good understanding of logic behind techniques, a feel of their essence, but sometimes I still feel some uncertainty because of lack of experience in teaching.

We train for technique first. Once our students have picked up the technique, we add-on to the basic drills with things like distance, timing and interception.

Heres one way we teach people lead kicks.

1st - Stand on one leg with your lead leg raised. Practice kicking a pad from this position, ensuring torque is generated from the hip.
2nd - Add in the "slide shuffle" footwork to the first drill.
3rd - Spar it with a partner.

If you didn't quite understand my example head over to the wednesday night group website and check out jeremy lynch - there is really good video of him demonstrating the lead hook kick there using the above method. And Jeremy has some of the best legs i've seen.

One thing about teaching is that you often learn as much or more from teaching than you did from learning the material when you were a student. When teaching your students, you have an opportunity to see the material from a third person perspective and this will allow you to notice certain elements, like the strengths and weaknesses of a technique or position.