How do I extract a downloaded sim from a Sims 3 pack and put it into my game? I'm trying to avoid using the launcher as much as possible.

Use this https://modthesims.info/d/364038/de...-sept-2009.html
if it turns into a .sim file then place it into your folder C:\Users\yourname\Documents\Electronic Arts\The Sims 3\SavedSims
If it just turns it into a .package toss it your mods\packages

What if it extracts a lot of package files with a long series of numbers and letters?

Those are other packages (cc) that were on the sim. I would go through those because depending on where you downloaded the sim (thesimsstore exchange) They could have broken CC attached.
https://sims3.crinrict.com/en/2014/...unterright.html this talks about it and if you click through crincrits site you will see more of the Bad CC. It's best to leave those off the Sim and until you have identified if they are bad or not.

also as a side note on this if you did get them from the exchange people have been doing CC Dump sims and those sims have contained lots, random CC, a ton of broken CC (not categorized correctly, causing errors, the famous broken cabinet, boots, and jeans) I went through a bunch of them just to see if they had any old CC that is hard to find and it was amazing at what some of these people uploaded. I'm not even sure they are aware that a lot of broken CC is attached to the sim.