New campaign - old school dungon crashing, lvl 8, 3 man party

[KorvinStarmast]

I'd recommend (as a party): (This is a kind of party optimization approach)
1 Fighter or Paladin; 1 wizard; 1 cleric
Note: at level 8, Fighter or Paladin is a matter of taste, but the fighter gets an extra ASI or Feat. I'd recommend Alert.

Make sure that one of the characters has the Criminal background so that they have thieves tools as a proficiency. Make sure the Cleric has the guidance cantrip.

Whether you take BM, Champion, Cavalier or EK is a matter of taste.

Note: Celestial warlock is a long rest healer, but, the 1d6 (your warlock will have 9 of them if you choose the warlock) healing light is a bonus action.

Why I'd suggest Life cleric: the channel divinity recharges on a long rest; it will be 40 HP to spread around the party and get them back up to 1/2 HP if you get into one of those "we nearly TPK'd there" fights.

Two available per short rest, though if you think you'll run into undead keep that in mind.
Wizard: control spells and debuff spells like slow. and (of course) fireball.

But, since you intend to play artificer:
Play artillerist. The canon's Temp HP is slightly over the top better than any other Temp HP option. It is a bonus action each round to create a buffer of damage before your characters take damage. Take a good hard look at that.