1st question- It cannot block anything, it is used to make noticeable attacks out of eye range and at the same time slowing down anything that the sphere makes contact with or vice versa. As for the gates, im too lazy to check the speed chart, but I think you can perceive 6th gate movements at your rank and in that case it wouldn't be able to significantly slow down the opponent's movement, but it does slightly slow them down, it would allow you to literally feel short range around you (3-5 meters I think) before your opponent makes contact. So if he somehow rushes from behind you and you use this you would be able to feel him enter short range around you
2nd question- Yes you can preform an attack right after, because as the jutsu is released it is out of your body almost like a shock wave moving outward