Int checks would be catch all for monster lore recollection? Why left put of rules explicitly?

Poison bug

Sage Advice: You can check Poison basic rule in Player’s Handbook p.153 that only describes: “…the poison retains potency for 1 minute before drying.” In Dungeon Master’s Guide p.257 some poisons could be very lethal if last for 1 minute (10 rounds).

My advice is that applied poison last until the weapon strikes or 1 minute is passed.

Do invocations like “Mask of Many Faces” or “Myriad Forms” require vocal and somatic components?

Beast Master Ranger balance

Sage Advice: Master Jeremy is right, it depends on context and your DM campaign.
If your adventure is in a multi level mega dungeon could be an hard task for Rangers, Druids and, if dungeon is very narrow, casters that can’t use their area effects/long distance spells.
But the problem could be similar in a city, where is more important to be sneaky or charismatic : area effect caster or Barbarians could be very cumbersome.

So my advice is to talk with your DM before campaign start and decide together wich classes could be better for all of you.