Snapshot Questions

We are planning to implement snapshots in Oracle.

I am looking for following :

1. Can we write to snapshot?

2. Can we create snapshot on the snapshot?

3. How many snapshots can we create on a table?

4. How does the optimizer works for snapshot? Do we need take stats on them as well?

5. do we see any issues with snapshots in daily usage? ( performance on database / any additional maintenance required other than space?)