Will the alien visitors start with helping with the clean up of the planet after first contact begins on our planet?
Yes, they will help us clean up our world.
They have far advanced technologies that will speed up the process of removing waste and encouraging rejuvenation.
The visiting races will not just hand us their technology for us to use, but they will use it for us themselves.
The secret government of this world has technology to shoot down alien spaceships, wouldn't the aliens have far superior technology to protect themselves from the secret government's weapons?
Yes, the visiting races have far superior technology to protect themselves from our secret military weapons, but accidents happen.
This speaks to the volume of visiting races, their drive and dedication to get information in to us, the number and frequency of visitation, and the tenacity of our government's hunt.
Will we eventually learn about alien life on other planets and their civilizations, and some of their technology through the internet?
Yes, we will eventually have access to all available true open information via world wide direct communication - the internet.
Right now we are allowed open access to mostly only untrue information.