If someone wants to be saved he/she must believe on the Lord Jesus Christ, being Catholic is a denomination of Christianity. When a person is saved he/she is a member of the spiritual body of Christ and automatically is catholic - because that simply means the universal body of Christ. A person can be part of Christ's body no matter what denomination he/she belongs to. Being a Roman Catholic sure doesn't guarantee that, that's for sure, but neither does being a Baptist!
No it is not. Denominations are abhorrent to God who did not want any:
That they all may be one, as thou, Father, in me, and I in thee; that they also may be one in us (John 17:21)
The Catholic Church is not a denomination. Baptists, Methodists, Presbyterians (all 100 of them) are denominations, and they are the ugly product of the so-called Reformation. The Church is simply the One Holy Catholic Apostolic Church that Christ founded.