Welcome Matt and Wife! We're so glad you found us! First let me tell you that every one of us in here has been in your shoes and lost new fish!! Second shame on the LFS Local Fish Store for giving you bad advice on two things. Yes you need bacteria, and selling you all those fish that would upset any established bacteria load.
So... a lot of things have been covered already, and you are going to read, read, read... right? I'm going to touch on a couple of basics not yet discussed, you may already know of some of this but just in case.
Your fish yes have suffered from shock and it comes in different ways but is quick.
All water needs de-chlorinator/conditioner to remove chlorine, every bucket, every water change. You will be doing minimum 20-30% weekly water changes, unless other issues arise, but this is basic care. Get a calender and write down what you do on what day, as time goes by and you forget when you last did something, or added someone to the tank.
Get a thermometer if you don't have one. Every bucket added must match the tank temperature.
Get a Liquid test kit as metioned in the previous post.
Test weekly at the least before and after your water change. Know your numbers always for ammonia and NI and NA.
When you have cycled the tank, and have good bacteria or bio load, (6-8 weeks) then you can add fish slowly. Even a large tank like mine at 75Gal , I cannot just go get 15 fish and add them, as the bio load is not sufficient to support that much of a change, and fish will die.
When new fish are added, float the bag in the water for 30-45 minutes and dribble littles amounts of TANK water into the bags every 5 minutes or so. You will equalize the temps and also acclimate the fish to any change in PH. We do not recommend changing the PH but it is important to know what kind of fish do best in what PH. Eg, my 8.2 PH in Ontario would kill Discus that need 6.5 - 7. so I have to look at African Cichlids or something locally raised in my area's water and slowly blend them over entry time.
When the time is up, you should have doubled the water in the bag and net the fish to put them in.
Lighting is important because fish need a natural fluctuation of light just like we do. As natural as possible. Get a inexpensive timer / power bar for your tank and set it to generally no more than 8 hours of light. Light can raise the tank temperature excessively, and cause huge amounts of algae. Setting the timer means less chance to overdo it. If you like to watch your fish till 11pm then set it to come on 3 pm, off at 11, and the rest of the time it just gets ambient light.
When you do finally add more fish do so 2 ish at a time. do it slowly as you currently do not have the good bacteria present. You need to keep building the good bacteria to support that many fish.
So lots to learn. Ask lots of questions! and after 15 posts come look for others in the chat room where we can talk live. Good Luck.