The one part of this is potions. Another part is group buffs you might get from members in a trial. There's things such as passives, poisons, or skills.

I would suggest cash builds. He is on YouTube and shows everything clearly for build

Google the UESP build editor and play around with it. You can get to 6.4K self-buffed, though most likely on a class that has Minor Brutality (DK) or Minor Sorcery (templar). Whether that would make for a good PvE build, self-buffed, is questionable, because you typically build for high crit% in PvE instead. You can easily reach that high weapon / spell damage, or more, in a group though. Things like:

• Group member (tank) runs Spaulder of Ruin.
• Group member (tank or healer) runs Powerful Assault.
• Healer runs Spell Power Cure (Major Courage).
• Tank runs Yolnahkriin (Minor Courage).
• DK in group gives you Minor Brutality or templar Minor Sorcery.
• I think there's an automatic 4-man dungeon buff that ups your weapon / spell damage.
• And so on, and so on (loads more).

In PvP you're aiming for short term self-buffs that will get you to such numbers briefly during your burst window. For NB these include, in no particular order, things like:

• The Merciless Resolve buff (+300)
• Attacking from stealth as a vampire (+300, may have been nerfed recently)
• Balorgh monster set (up to +500) or Magma Incarnate (+215)
• Clever Alchemist set (+675 from 5-piece)
• Continuous Attack alliance war buff (+10%)
• Major Sorcery / Brutality (+20% goes without saying in both PvE and PvP)
• Master Bow (+330, though not on stat sheet)
• Infused back bar enchant (+452 for 5 seconds)
• Sea Serpent's Coil (+430)
• Vateshran 2H weapon (+300)
• Simmering Frenzy (+400, vamp skill, not sure this still works as advertised for ganking. I believe it was nerfed.)

The percentage buffs, e.g. Sorcery / Brutality, Continuous Attack and medium armor mean the flat buffs are worth more than they look on paper.