Yeah, the levels on the Archon Hunt are comparable to Sedna or the Kuva Fortress in SP (130-150), but with respawns removed. The first planets of SP are only 100.

Primary arcane adapters cost 25 steel essence from Teshin, which is the exact amount of essence you get from doing the 5 daily steel path incursions. Put them on any gun you like, you can always farm more.

Yeah, I'm talking about the original Incarnon weapons from the Zariman, which are distinct from the new Incarnon Adapters you get from the Circuit. You can buy the blueprints from Cavelero with Zariman/Holdfast rep.

Rhino should generally be fine for an Archon hunt, you just need to get good at charging Iron Skin on enemy damage so that you're not constantly recasting (that is, don't cast it until you're in combat so you can build up a big buffer, rather than casting it before you get in combat).

Revenant plays similarly. Mesmer skin has a number of stacks, where any damage removes a stack and gives you a couple seconds of invulnerability. With about 15-20 stacks from a normal cast, that's ~30 seconds of invulnerability if you're constantly getting hit and usually more if you're moving around and dodging. Nezha is just Rhino but faster and more slippery.

Edit: Oh, liches/sisters. Yes, Tenet weapons are from Sisters of Parvos. I'd put them below steel path in terms of difficulty (enemy levels 60-100). Progression-wise, while you don't have to do it before archons, you'll definitely find it easier. Lots of good weapons in both pools.