This is going to be made immensely difficult by the simple fact that there is no such thing as "Protestant Christianity". The term "Protestant" is a pretty loose umbrella term that encompasses just about everything that came out of the Reformation and since--from Lutherans to Presbyterians to Mennonites to Methodists to Baptists to Quakers to Adventists to Pentecostals to Non-Denominationals. And, trouble is, that compare Lutheranism to the Baptist tradition and we see they are quite different, in fact there is a far bigger difference between Lutheran teaching and Baptist teaching then there is between Lutheran teaching and Roman Catholic teaching.
It's better to instead think of there being Protestantisms, rather than a single Protestantism. Because "Protestant" ends up mostly being a kind of catch-all label.
Roman Catholicism teaches that salvation is by God's grace which we have on Christ's account which through the Holy Spirit in us we cooperate with in order to love God, do good works, and live in faith. That is, salvation in Roman Catholic teaching comes from God working in us and we cooperating with His grace by the power of the Holy Spirit to live a life of faith and good works. This differs from many/most Protestant schools of thought,
Lutheran and Reformed theology (Presbyterianism is Reformed) holds that salvation is a monergistic work of God (meaning God acts alone) rather than a synergistic work (God and human beings cooperating together); and that salvation is by God's grace which we have on Christ's account which the Holy Spirit works in us as faith through which we are justified, and thus we are saved by grace alone through faith alone.
I'd say that if your friend really believed in salvation by grace alone through faith alone on Christ's account alone, then your friend shouldn't doubt or question the salvation of Roman Catholics because if salvation by grace alone through faith and Catholics have faith in Christ then they are saved. By suggesting that Roman Catholics aren't saved because they have some wrong beliefs is to deny salvation by grace alone through faith and to say that we are saved by what we do, think, say, or believe--in this case, by believing the right things, which is salvation by works.
Yes, you can attend and visit. But you won't be allowed to receive the Lord's Supper. In Catholicism one must be a Catholic in good standing to receive Communion. But no one is going to prohibit you from visiting and seeing what a Catholic Mass looks like first hand.
See above. There are different terms for this: Holy Communion, the Lord's Supper, The Lord's Table, and the Holy Eucharist.
Generally, Protestants don't see it as being beneficial to ask the angels and saints to pray for us; but it depends on what kind of Protestant you talk to as to why. For example, in Lutheranism we say that since we cannot know for certain that the saints and angels can hear us that it is perhaps preferable to not ask for their prayers (they might be able to, but we can't know because it's not revealed to us one way or the other); however by the same token we do believe that the saints and angels DO pray for us nonetheless. So even though we don't ask them to pray, we believe they in fact do pray for us anyway. Other Protestant traditions will probably argue that since the Bible is silent on all these things one shouldn't believe them at all (again, it depends on who ask).
St. Joseph is honored (by Catholics and other Christians alike), but the reason why the Blessed Virgin Mary is so honored (not just by Catholics mind you, but also Lutherans, Anglicans, and Orthodox as well) is because she is the mother of Christ, she bore God in the flesh in her womb for nine months and then gave birth to God in the flesh. Thus we honor her in the way in which Scripture confesses, calling her blessed among women (Luke 1:42) and the highly favored of God (Luke 1:28); we call her Theotokos ("God-bearer") and mother of God because Jesus Christ, her Child, is true and very God. She is the blessed virgin mother of God, blessed among women, her womb as sacred as the ark of the covenant and the Holy of Holies itself for it housed God Almighty Himself.
No. Though generally Catholics recognize that people will be judged on the basis of what they know and the good they sought to do based on what knowledge of the truth was available to them; and thus if one never knew Christ through no fault of their own, that will be taken into account at Judgment.
Catholics do evangelism. But evangelism doesn't necessarily look the same way among more traditional churches as it does among modern Evangelical types of churches. Evangelism is chiefly about preaching the good news of Jesus, not trying to ruthlessly convert people to Christianity or beat them over the head with a club.
-CryptoLutheran
