a couple of venting questions

hope you guys can help. just purchased our first house,a straight ranch slab house in mass.i have noticed some things now that the colder weather has arrived.
1. the dryer is vented into the attic and then over to the soffet.its about 4 inches from the soffet vent for the attic.now i notice when the dryer runs for a while the vent drips from the condensation outside. is this normal or is this dryer vent too close to the soffet vent for the attic?

2.we have central air,i noticed that the heat comes out of the vents close to the floor but i have a big vent on the hallway ceiling that sucks air when the heat is on.since heat rises isn't this vent sucking hot air back into the system?

3. there is a pvc stack out of the roof with an elbow at the end.i noticed now that when the heat is on condensation comes out of the end so im assuming thats the exhaust for the furnace, we have all gas.when the furnace stops for a while i notice a icicle hanging off the end, is this normal,

any info would be greatly appreciated thanks.