Well Azunyan has actually played as a dark stalker so her advice is more reliable, but I'll give it a go.
VITSTR is a sturdy build, but unbelievably slow. I would recommend STRAGI for training until 80-ish.
You should go all STR for both builds until it's around the 60 mark (the last big jump in stat increase), then go VIT or AGI depending what you want to do. 20 dex is pretty much what you'll need at any point in time, unless you PvP. INT/MAG is useless on PvE as well, you don't need it unless you like being strange.
Increase Maximum HP lv5
Inxrease SP Recovery lv5
Spear Mastery lv5
Increase Spear Accuracy lv5
Spear Delay Cancel lv3
I don't know what skills you use for Knights/Dark Stalkers. I believe with just 2H spear mastery and Double Thrust you're good for training.