2. SACLOS means you have to keep the crosshair on the target in real life in order for it to hit (TOW, HOT, Dragon) and had wires trailing behind them while it flew. Essentially the weapon automatically flew but still required human control. Today's weapons like the Javelin and equivalents only require a lock. As far as SF2 Gameplay I've never played with it so I have no clue if it really makes any difference other than restricted firing arcs or the like.
Inertial Homing = the weapon has a database of the terrain the weapon is to fly (Tomahawk, ALCM, ACM, so on), not modeled in SF series as a whole
Radio Command Guidance= Requires a radar to lock onto the target, and provides mid-course and terminal data (I'm assuming while locked the radar is "painting" the target for this) for the missile, same as in real life.
Beam Riding is laser-guided and in real life requires a laser designator and also in real life (best example would be Laser Maverick, Bofors RBS70, Hellfire, etc.)
3. I'm not sure but may be encoded into the Weapondata.dat file that is associated with that weapon so when the game reads that file, it applies those values without putting them on the appropriate Data.ini
4. Perhaps because SF series doesn't properly model the terrain following flight characteristics of a cruise missile which realistically game-wise point and shoot.