This build is geared for both pve and pvp.
Weaponry and Equipment
R1 Lost Saif +10:
1x Cold Abyssal Radial (+65 arc scaling) w/ 6% open attack secondary
1x Cold Abyssal Triangle (+65 arc scaling) w/ +15 flat bolt
1x Bolt Abyssal (22.5% bolt atk up) w/ +33.8 flat bolt secondary (doubled effect)
R2 Beast Cutter +10
2x Cold Abyssal Radial (+65 arc scaling) w/ 6% open attack secondary
1x 27.2% elemental triangle of your choice (fire recommended)
L2 Loch Shield
L2 Hunters Pistol +1
1x Pulsing (5 hp /2 sec regeneration)
anti-clockwise %20 / oedon wraith +3 / communion +5
full choir minus the headpiece if you want to look as mage as possible
Other weapons to consider:
lost bolt hunters axe using a bolt abyssal for double rally and a tri cold abyssal with rally secondary stacked
It's fun to use loch shield if you can adjust to augur for parries. With it you can tank hunter tools decently and completely shrug off 50 blt evelyn spam. The downside is you have no real way to punish people for attempting to heal outside of what your hunter tools can do for you. So the choice is up to you whether you want loch or a hunter's pistol.
Saif is amazing at baiting attacks and aggression between its untricked R1 -> L1 combos and regular tricked R1s which cover lots of ground.
If you oil enemies up and use a fire gem on your beast cutter, hitting them with a single strong attack from range can do devastating damage. Your best bet is either rolling -> L1 from untricked or backstep R2 from tricked. It has good enough tracking that you can manually aim it while unlocked as well. The R2 in particular is very uncommon to the point most people don't even know it exists.
Beast Cutter really shines when you trade with it because, while its R1s lock you in place with a long recovery time, you just can't be interrupted at all and have fully hyper armor.
Any number of hunter tools can be used to great effect since they still scale well beyond 50 arc. Blacksky, executioner's, augur and brew are all good choices.
Saif and beast cutter are chosen for a number of reasons. Quality weapons in general tend to make decent arcane weapons because of how arcane scaling is calculated. These two have very low requirements (only 3 points of investment to use them both).
Saif, as your primary means of damage, is ideal as bolt for two reasons. First, of the three types of elemental damage, bolt is the only kind to have gems with a double secondary. Therefore you can stack the double secondary with flat damage and an additional gem with flat damage for a total of up to 48 flat bolt. Because Saif's fast moveset and not so great modifiers, this will get you highest potential damage. Second, aside from henryk's set, it's fairly difficult to get good bolt resist so vast majority of players will have lower bolt resist than any other element.
as a general rule for any weapon on an arcane build; for bolt you want lost variants. For anything else, you want two radials and a tri.