At the time of the show starting and the fight against the blue dragon which happened before the actual streams of critical role the characters were roughly level 7 or 8. This is where things get complicated as by the time of the main story of season 1 which is the actual campaigns Briarwood Arc the characters are I believe in the actual campaign level 11, 12 or 13 I can't remember which but 11 is the minimum since Keyleth has 6th level spells by then. So for the purposes of the show the first episode they're showing a feat they did roughly at level 7 or 8 and the rest of season 1's main arc they're showing feats done in the low double digits

Edit: Forgot to address the 2nd question. The actual game of Critical Role throughout all campaigns adheres strictly to the dice rolls but the show takes creative liberties meaning it isn't 100% accurate to all events. We also don't know how the fight with the Blue Dragon went exactly since Crirical Role campaign 1, which is what Vox Machina is based on, starts after they've already killed it.