What happens to us after we die?

waseela's are definitely used by people in Islam.You dont need to open a topic if u understand this example.
Hazrat Muhammad (SAW) asked Hazrat Awaais karni (R.A) to pray for the forgiveness of Ummah of Hazrat Muhammad (SAW) and thus made Hazrat Karni (R.A) a waseela for his Ummah.
If you still want to discuss is upto you.

Recently,people use waseela as Aulia-Karam and go their shrines and ask Aulia karam to pray for them. Going to Aulia-Karam is not shirk, search online otherwise discuss.

Since only Ilm-ul-Ghaib is known by ALLAH, a part or any part of it can be shared by anyone whom ALLAH desires. You and I maynot know,we are worthless creatures, but pious people of ALLAH surely know and can help in this regard.

It has been related by ad-Daylami on the authority of Abu Hurayra who said that the Messenger of Allah, may Allah bless him and grant him peace said:

“Indeed from knowledge, there is a part which is concealed, which no one knows it except the Knowers of Allah. For when they speak on it, no one rejects it except the people completely heedless of Allah.”