1. Is it possible to just tell task group to go to curtain system without clicking through each jp in orders menu ?
No.
3. How many tech trees can i research without falling behind on important things ? Should i mostly concentrate on one weapon type ?
Depends on many, many things. Your doctrine, industry, wealth... There isn't One Right way of playing. You just do what You can in the best way and win or not. Best way to evaluate Your results is by playing. For example our enemy can have superior tech but you can destroy him by numbers.
For most players main weapon is missile technology. If You feel that You have enough advantage over Your opponents in it, You may "go into" others weapon techs. (This is my way of playing, but Everyone have their own ways...)
Essentially, like in real live some of Your techs will be above and some below the level of the enemy. Strong economy let You use more research facilities, build more sophisticated weapons and specialize ships for special purposes.
2. What is best solution for watching jp's ? Keeping scout or starbase on every jp bloats tg list, i have already 15 of them and its growing fast.
Personally I use stealth ships witch passive sensors. But only in most risky systems. To place TG on list lower just add XXX in its name or something like this.
Maybe You can use buoys but i never tried that.
Sorry for my simple-English.