I am going swordsman > x > peltasta > rodelero C3, should I get peltasta 2 for high-guard or can I go highlander to help me questing ? Going peltasta C2 is worth it for PVE tanking ?
Thanks
Swordsman3 or Peltasta1Hoplite1 imo
Personally I like pel2 because it no longer feels like such a waste to take it just because of the taunt. You can now do some ok damage with Umbro Blow and Rim Blow when High Guard is up. Then if its just for dps, you can swap weapon and get rid of High Guard. Use it as a burst on a 1 min CD. If you are tanking maybe wait 12 seconds and to a second rotation before you switch it off.
Just remember to always use your Rodelero stuff before so it will be on cool down during High Guard, you never want to use any damage skills but Umbro Blow or Rim Blow during High Guard 
I’m pel2 + cat, so I switch to 2h spear. But since you will be using sword and shield you can swap to just the sword and back again, a bit more tedious but works 
It depends on what you are aiming.
For example, I’m making a CC heavy swordsman for team battle (once it gets released).
Sword -> Pelt -> Pelt -> Rod -> Corsair -> Fencer/Rod -> Rod
Hop 1 for spear, Highlander 2 for raw damage or Pelt 2 for swash slaving.