It is recommended to have one character at least at lv 55 (only concerns the main weapon though).

You can buy all of those at the calpheon city armor trader. His name is Grandus and he is very close to the storage NPC.

Total cost 1m 500k for accessories. Ultimate dobart +5 = 2m and 200k per gear part, a total of 11m. Usually you obtain your own Black Stone (Armor) though, so 1m 100k per gear part, a total of 5m and 500k. No chance for failure. Your defense (DP) will then be as you see it on the first pic. One gem slot only gear, you will want to get 2-slot armor like Grunil as soon as possible.

A full Asula set is recommended. They can be obtained at: Abandoned Iron Mine close to Altinova (Necklace), Earrings and Rings (Helm's Post close to Heidel), Belt (Elric's Shrine close to Heidel).

Black abyss which is almost as good as a green DUO weapon but way cheaper. With one of your characters at lv 55 you start a quest series called [Lv55] King of the Arena. You will find the start NPC via O key -> Suggested tab and then scroll down a bit. Follow the quest line. The Dobart armor should keep you from dying to the opponents, if not get some defensive food, Elixir of Will and HP pots. After you got something better you can exchange its class type at an Altinova NPC and use it for an(other) alt.

Sub-weapon. There is no good cheap alternative sadly. The dim weapon is bad. What you see here is the AP model for this class (Sorc).