1.) Dormant jump points still exist. What is going on is basically fluff to describe something that the game needs to function. When a new jump point is explored the computer generates a random number for the destination system. If that system already exists it checks to see if any jump points remain that do not have a destionation. If so then it connects to one of those. If however all existing jump points go somewhere (ie have been explored) it creates a new jump point. Once created it can be found by either observing a ship transiting, or by resurveying the system. This is different from Starfire where this program originated in that a "dormant jump point" was never detectable by surveying, only by watching a ship go through it.
2.) Yes, JG after a a jump point means that there is a jump gate installed, and yes they can appear randomly.
3.) There is no actual distance between systems on the system map display. The best tip I can give you is try to use some system that makes sense to you. I usually start with the home system in the center and have it's jump point connected systems radiating outwards. And yes there will be some strange connections that make a mess of the map. Good luck.
4.) It is not so much the number of systems that you have explored that says whether or not you should find aliens, but how many habitable planets in those systems there are. The requirements are fairly tight and only a fraction of the planets will be habitable from the start. Just for example any planet with toxic gasses will not even be considered for aliens. The grav range is fairly tight, IIRC about .5-1.5 G, ect. There is a thread somewhere on the forumn where Steve gives the formula's sometime this year.
Brian