Stall Teams?

Read here :
https://grandorder.gamepress.gg/zombie-team

Actually I am not fun of Stall team since It is ANTI-BATTERY and for me Time is More Valuable than Money. My best attmept is SAber war Mashu+Tamamo+Waver against MHZ without event CE, ~60 turns.
However I can recommend some tips for you and others since Stall team is in fact one least expensive team.
More detailed you can check Zombie team
"https://grandorder.gamepress.gg/zombie-team"

The goal of Stall team us commonly using defense+heal (and team invulnerable,evade, and taunt)
Therefore normally a Stall team include servants with Skills and NP spam in order to enhance defense for team and healing. Typical servants include (representative):
Mashu: Best Kouhai for best team coverage, and Taunt
Jeanne: Team cover/Healing, typically after her NP strengthening, and unique class advantage
Hans: better potential NP spam for defense up and healing
Irisviel/Medea Lily: Huge healing capacity.
My beloved Tamamo: Unique NP.
Martha: healing, debuff remove and buff removal.

So you can see a common trait is that generally these servants are 2-3 Art card therefore it is better for Art chain and NP spam.

A famous MEME team is Hans/Dual Mashu 160+ turns killed 12 guts Herc in Nerofest, as picture shown. Even his support Mashu isnt 3-10 and lv70 yet

However, it doesnt has to be all 3 servants in team functioned same for healing+defense only. Debuff to enemy also required for some circumstances live reduce Critical chance and Reduce charge. Then, other servants can also be applied in Stall team,
like
Waver+Jeanne+Tamamo: Waver can provide team cover defense and NP charge, and NP may stun/reduce charge to boss. Tamamo is the engine of team. Jeanne can also Stun enemy boss
Vlad+Merlin+Tamamo: 2-100%-charge reduction skills. And also, Merlin+Tamamo 4060=Ultimate NP spam and star generation (Art Critical=NP gain twice). Therefore it doesn't matter even Vlad is Berserker
Nightingale: Some people said that Nightingale is kind of fragile due to class. Off course, but like Vlad, in a good Stall team she can be extreme good to bring down enemy damage (1st skill+NP)
Orion in Art team. why? Orion's skill are quite stronk for self-defense, and her NP has one best debuff effect to enemy boss.
David/Tristan. Team evade also count on Stall.
Kiritsugu: Targetable Taunt with only 5 turn cool-down. Could be compatibility if another team has self-evade skills. And NP has charge-reduction effect
d'Eon + Tamamo: this could be the best Taunt team since d'Eon's unique ability and remedy by Tamamo (or Jeanne and Nightingale as other member). Geogies could also worked in same way.

So you can see we dont have to specific focusing on all 3 team members should has defense+healing skills/NP and are Art-only servants. Such teams with Orion/Vlad are still quite Stall in long tough boss fight, like 1,000,000 multi-hp bar boss in the future.
And also it is definitely not recommend for fighting against any Piercing-Invulnerability or Debuff-removal boss. The reason is simple: Stall team required strong defensive buff, so off course not facing such boss. Like it is crazy using Waver+Jeanne+Hans against Drake or versus Oni.

Other specific Stall team include:
Cus (no matter which Cu)
Nero OG (one best self-defense-gut servants. Save the team as final member versus Lancers)
Marie: Close to Nero and Cu in specific fight.
Herc with bond CE
Leonidas NP spam. Or specific team for him (Targetable evade/Invulnerability/healing)
Bond CEs, Like Liz, Medea Lily
Dual Geogies
Charm team of sisters: ANTI-MALE, can be considered as Stall team if that Male boss has very high hp.

Etc.

Nerofest was really a lot more about needing one or two particular servants to clear challenges rather than needing certain team builds.

Also as a warning, when Merlin arrives, everything will be buster/crit. But to answer your questions:

1. To take little-to-no damage while slowly whittling down the enemy.
2. Jeanne, Waver, Tamamo (caster), Mash, Hans.
3. Use them when you run into a hard bossfight that you can't just throw damage at.
4. Yes. Evade/Invulnerability/Healing are the staples of stall teams.