1. Goku giving Cell a senzu beans can be justified since he was right about Gohan so that can be forgiven.
2. Him Letting Fatty alive was risky but only because he felt that it wasn't his job to do finish to job so he let the kids to do it themselves since Goku won't be there forever. After all, the kids have the tools all they have except experience which what Goku miscalculated.
3. That was really dumb.
4. No comment
Answer is 4.