What are some helpful hints or tricks to keep me alive or things to bring along. I have some friends that go quite a bit and have all the ropes and such. I borrowed a harness from one of them for my first time. It was pretty fun so I went out and bought a harness, ATC and a few locking carabiners. I am super paranoid about going down the rope and running into a knot or something in my atc. I feel like it's a death sentence or something.

This is harness I bought after trying a few on and reading reviews. I am going to try out my new gear this Saturday with my buddies. I am 6'3" at 245lbs. So I am kinda fat.
https://www.backcountry.com/mammut-ophir-4-slide-harness-mens-mam003l
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You might try rappelling instead of repelling. Repelling is easy enough and you don't need special equipment.
Sounds like you found a fun new hobby. Congrats.

I detest those design harnesses for rappelling. Too much distance between the leg loops and belt tie in, so that the belt rides up far too high. That design is intended for fall arrest for climbing.

CMC Rescue has some good harnesses. What I usually use now is a Petzl Navaho but it's apparently been discontinued.

I also suggest getting a brake bar rack for rappelling. It's a lot smoother and more controllable, adapts to various weight and rope types, and is easier on the rope.

Outdoor Research and AMGA has a few nice videos on how the basics of climbing/rappel

Here's one: Video Link

Quick things I always do:

1) Tie knots on both ends of the rope so you don't rappel off.
2) Tie knots on both ends of the rope so you don't rappel off.
3) Friction hitch with some accessory cord and a spare carabiner. Gives you a 3rd pair of hands that work even if you get distracted or knocked unconscious.
4) Make sure you inspect and trust your anchor. Make sure the links on the anchor arent about to rust through; that the bolts aren't loose. If using natural anchors, make sure they're rock solid and won't shift. Redundant anchor points is pretty crucial.  
5) Optional, but nice: get a personal anchor system (or sling) and set up an extended rappel, as shown in the video.
6) Optional: if unsure of yourself, have a friend up there to make sure you're tied in correctly, and have someone give you a fireman's belay at the bottom. Work up your confidence.

Nothing wrong with that type of harness for the rappelling I do. Full body harnesses are mostly just impractical for sports/trad climbing or mountaineering due to weight and bulk IMO

From a canyoneering standpoint you want a harness that you can walk in for short distances sometimes.  I am also a bigger guy and prefer wider belts with padding.  I personally use the Petzl Corax because it fit me best and was easy to use and its design means you dont have to thread your buckle every time.

With wet rope friction is your friend.. minimum I like the black Diamond ATC-XP if you want and ATC type device, There are also a few devices that allow you to dial the amount of friction you want.  The Sterling ATC as well as the Petzl Pirana.  And of course each company out there usually has their own versions of each if you prefer a particular brand.

You also always want a autoblock of somesort in addition to your descender, I just use a prussic on a locking carabiner.  My rappel device is actually further out on using a Sterling chain reactor so that say i rap into water, it is up by my chest to aid in disconnecting once im getting off rope.

Also make sure your static line is ok for water, some does not like water and soaks it in.  There are some great canyoneering specific ropes out there.. I prefer bluewater or sterling myself.

Also learn how to setup a retrievable anchor, it can be done right and wrong.

As for knots, unless you tie one mid rope and throw it down, dont worry about it.  BUT if you have to tie a butterfly knot for a jacked portion of the rope, or connect multiple pieces of rope, there are procedures for going around them that are pretty easy to do.

If you have a buddy that took some classes, that is awesome, if not, take one, you will learn a TON and have a blast as most canyoneering classes prefer short hikes and lots of raps for their training!

I used to go a few times a year, but have not for a few and I miss it.

Random thoughts:

Running into a knot is FAR better than rappelling off the end of the rope which accounts for more deaths- including some very experienced climbers- than you'd think.  I lost a friend probably ten years ago now who did that; he was a really good climber but he and his partner where trying to get off a rock face as a storm was rolling in and he apparently didn't tie a knot in the ends of his ropes.

Take at least a basic class.  It's great to learn from friends but it's not uncommon for people who've been doing it for a while to do stuff unconsciously and not mention what they're doing.  Use a checklist the first couple of times out if it helps you- there's no shame in being safe when a mistake can be extremely painful and costly... or fatal.

Take a rescue class.  In my experience most folks know a minimal amount about rescue techniques nor do they carry enough gear to do a simple rescue.  Not saying you need a full high angle rescue course, but have some basic knowledge.

Always do a visual inspection on your gear before each outing and retire any gear that is suspect.  Always double check your harness tabs (make sure they're doubled back per the manufacturer's instructions) and all knots.  After you've double checked yourself, do a buddy check where you check each other's gear.  It takes thirty seconds- which is a lot longer than the eternity it'll feel like waiting on rescue with a broken bone (and not all rescue squads will have a paramedic who's carrying some form of pain reliever).

Do not step on your ropes.  Canyoneering gets ropes in the dirt a lot so you don't want to grind it into them.  Clean your ropes and gear when you get home.

Always check the weather for the area where you'll be as well as upstream.  Remember it can be bright and sunny where you are but a sudden shower upstream can cause a flash flood where you are.  The weather radar tracking apps are really handy for this.

Don't get in over your head; know your limits and know when to say no.  Plan you route(s) and let someone know your plans.

Carry a 1st aid kit and know how to use it as well as improvise.  A wilderness first responder class is really helpful.

Carry water and a water filter but don't count on seasonal water to be there.  Some routes you can stage water but write your name on your jugs as it's not uncommon to find other people's jugs stashed in the same general area i.e. under the only clump of brush in the area.

Wear your brain bucket- I'll admit I wasn't always the best about wearing mine but they weren't as common, or as comfortable, as they are now.

Have fun!