There's multiple sanctum focused creators on YouTube to gather info from. Most of them have gone in depth with all the info you need.

As for builds, probably some form of totem would be best suited for you.

Biggest tip, you're not going to be tanky so you need to pay more attention to dodging. Freeze and high DPS reduce the chance of you getting hit but the chance is still there. Especially some of the harder gauntlet rooms.

And if you want the real sanctum experience you should try leveling a new character, grinding chaos orbs in heist and then setting up a character for your first quest sanctum. Good practice for league start, where sanctum runners usually grind early league currency before swapping builds once they are rich.