And what are the basics of number 1, in your opinion?
There is a postive and negative aspect:
1. Postive
The simple realization that one is a sinner in need of salvation from sin and that simple faith in what the true God has provided in the true Person and work of Jesus Christ is completely sufficient to save you.
2. Negative
There must be no conscious denial of any essential aspect of what is listed above.
For example, any denial or distortion of the God of Scripture. Any denial or distorion of the Christ. Any denial or distortion of the provision for salvation.
In 1 Corinthians 15 there was a denial of the resurrection of Christ.
In Galatians there was the addition of works to the gospel and thus a denial of the sufficiency of Christ's atonement.
In my opinion if there was conscious denial of the penal substitutionary atonement of Christ at the point of professed salvation, that salvation is invalid and false.