Having acknowledged the potential dangers can make it harder to astral project being that fear grows and can hold you back from succeeding. But that doesn't mean ignorance of the dangers is bliss. So first off, don't let the dangers grip you with fear and hinder you from astral projection.
As for protection you can do a protection spell, ward, and/or shield. You can also use some crystals as a means to protect you. (If you choose this route this is a good way to study crystal and stone properties to learn about them as you find one to use for protection). You could also enchant an object, such as a pendant, ring, etc, ti protect you from harm as you astrally travel.
Being a believer in Norse religion - Heathenism - as you say, you can do a Hammer Hallowing, invoke runes for protection, draw runes or bindrunes on your body for protection, wear protection talismans of bindrunes/runes/mjolnir. Or you could invoke a deity and ask for protection as you project.
Either way you go there are many ways in which you can protect your self.