The "Augments" transfer from class to class. Some classes have overlapping skills/abilities which will also transfer over. Examples of this are Scarlet/Hundred Kisses transferring between Striders/Rangers/Assassins and Ingle/Brontide/Affinitiy spells between Magi and Sorcerers.
If I were you, I wouldn't worry too much about trying to get a mage for healing. You're better off buying potent greenwarish in Gran Soren and living off the land. Two sorcerers would be of greater benefit IMHO.
All the core skills will carry over, so all the dagger specific ones like double jump and the dodge one will work for assassins as well as strider (provided you have daggers equipped as an assassin, rather than sword) and levitate, magick agent and focused bolt are shared by mage and sorcerer.
When you look at each skill on the learn/set menu there should be icons indicating which vocation that skill applies to.
Augments, of course, can be used whatever vocation you are once you've got them.
Thanks to the advice I've received here I've got more focus and understanding of the system and am now picking and choosing the skills I'll be bringing with me to the Assassin and Sorcerer skill trees.
And I've also found that my Pawn Millenia is being constantly used by at least one player. *Sniff* It's so nice to know that there is at least one person out there who is taking care of my little girl!
...Actually, not so little and a full fledged woman. But even so!
Even though there are "optimal" classes for developing physical/magical attack (i.e assassin and sorcerer), you'll still want to level up other vocations strictly for their augments. For example, it is useful as an assassin to also level up fighter and warrior to their max for the physical attack bonuses available.
There are ways to level up vocations without leveling up your character's actual level. The most obvious way to do this is to wait until level 200 (max), but there's an easy way to do it before then. Ask about it when Gran Soren... changes.