So i am rebuilding my Bard to be a Lore Bard in the long haul, and im looking at all the spells i could attain. I looked at the wish spell and it said i can replicate any said spell from 8th level down, so theoretically speaking, could my Bard cast a spell from any classes spell list? Examples such as Find greater steed (since it has no duration) or Investiture of Flame (just cause)?
The basic use of spell allows you to cast any spell you want, from any spell list, up to 8th level. This could be an 8th level spell like Demiplane or a 1st level spell like Magic Missile cast at 8th level.
For the spell you replicate you: ignore casting time, ignore all components, ignore any other restrictions. If the component is part of the function of spell like the chest in Leomond's Secret Chest or the sapphire of the Dawmj's Instant Summons then the Wish creates that component for as long as the spell is in effect (some DMs may allow you to just have the component permanently after afterwards, discuss with DM). There is debate on whether the replicated spell will require concentration - you will need to discuss DM as there is no definitive answer the RAW can be interpreted either way by the words used (and annoyingly Sage Advice refuses to answer despite many, many, pesterings).
Essentially you are casting a 9th level spell as 1 action requiring only the Verbal component. You just get to choose the spell effect by copying any spell you want at 8th level in power.