The stack and Venturing

So i have a [[Sefris of the Hidden Ways]] deck and was wondering when all the triggers would go on the stack with multiple venture triggers on the stack because i want to know if i could loop the Undercity easily or if its alot more luck based then i hope. In this scenario I have Sefris, [[Hama Pashar, Ruin Seeker]], [[Radiant Solar]], and an undercity on the second to last room (lets say Archives) and i cast [[Nadaar, Selfless Paladin]].

When Nadaar enters i get 2 venture triggers from them and Radiant Solar, i go into TotD3 and reveal the top 10 and hit a creature that enters to give me the initiative (such as [[Underdark Explorer]]). I looked other places and it seems that the new ETBs (initiative and Radiant's venture in i believe which order i choose) would trigger first before either the second TotD3 (from Hama), the Sefris reanimate (for completing the dungeon), and the second venture (from Nadaar) would resolve.

so is that correct and all those triggers remain on the stack in that order until everything else has resolved (the sefris getting interjected once the second TotD3 resolves) or is it one of these other scenarios

2. both the TotD3 triggers and Sefris trigger before the new ones go and start resolving (if so in what order or would i get to choose the order of any ETB's this way) (this is the way i first thought but after a bit more research don't think is correct)

3. the 2 TotD3 triggers then Sefris then the venture that has been waiting before the new ones

so mainly would i have to hit a creature that ETBs to give me the Initiative with the first TotD3 trigger to loop or could it be a slightly different trigger to still work