Caught a couple first time out. No monsters but really enjoyed the process, I�ll keep practicing and hoping to post some good pictures.

What�s better to eat? Medium sized or the real big ones?

Small to medium size under 15lbs

5-8 lbrs.......

You might also consider going to a catfish farm. You do pay by the pound for everything you catch and maybe a small entrance fee. You can pay a little extra to walk out with filets.
No messing with boat or fuel charges which offsets or is more than the fish cost.
Fishfarm makes their living on you catching fish so you are going someplace with very high likely hood of catching catfish.
Ask the staff where to fish, what to use, .....
Usually have worms and shrimp for purchase there.
Most of the customers are pretty friendly and can give you some pointers about what is working for them.
Get used to catching a few in this environment then go out to the lake where you can add in locating the cats.

When out on the lake if planning to stay in one area, you might consider throwing out one or 2 juglines while you are fishing from the boat checking on them every once in a while. Put in on upside of cove and let drift across while you are fishing.
Following link has very simple and inexpensive jugline setup(could be cheaper by using a gallon jug for float and using rubber bands to hold hooks when not on water.) Bait with blue gill/shad, stink bait, liver, shrimp.
http://www.louisianasportsman.com/details.php?id=10731

I usually have one line out under a large cigar float when I paddle my kayak over to check on my jugs and sometimes hook a cat while I am untangling jug, rebaiting or getting my cat off the jugline.

You got a good intro from being out with the guide, now go out and fish.

For a first inexpensive catfishing rod/reel check out the Shakespeare Ugly Stik Catfish Spinning Reel and Fishing Rod Combo at Walmart.
Or for a rod that will work for small cats plus bass, Shakespeare Ugly Stik GX2 Spinning Reel and Fishing Rod Combo

If you're targeting blue cats, nothing beats fresh shad. Get a cast net and learn to throw it. If you can budget for it, get a bait tank. If not, you can fill a small cooler 1/2 full of ice and just throw the shad on top of the ice. I think live shad are a little more effective, but have caught plenty of blues on dead shad.

I like using 3/0 or 5/0 Kahle hooks and 20# leader. Main line kind of depends on the capacity of your reel. I use 12# on my spinning reels and 15# on my baitcasting reels. Again if it fist your budget, nice baitcasting reels are the way to go. A catfish big enough to strip the drag on a spinning reel can leave your line extremely twisted by the time you land him.

Run Braid ........