I rescued a snake who wasn't taken care of very well

Hi all!

So just today I rescued a corn snake that's about 2 feet long. His previous owner unfortunately took his own life, and so I've adopted him. He's in a 20 gallon tank (I think; it's bigger than my 10 gallon and smaller than my 40 haha), and he came with a water dish, a few fake plants, a potted cactus, a hide, and an under-tank heater (with no thermostat or thermoregulator). I of course want to give him the best care possible. I fed him today one a fuzzy and a pinky, because that's what I had. He seemed very hungry, and probably hadn't been fed in a while unfortunately. I'll weigh him soon to see how much I should actually be feeding him and how often. Because he hasn't been handled much, he's a little skittish.

Now that you know what's happening, here are the questions I have:

1) Should I plug the heater in or not? I'm afraid, because I've heard horror stories about heaters burning snakes, and I definitely don't want to do that.

2) The snake came without any lid holder (not sure what they're called), like the little clips that keep the lid on the tank. I had some from another cage I'm not using, but it's a 10 gallon tank. Will it work for the 20 gallon still?

3) Is having a small live cactus in a snake's cage dangerous? I don't want him to get pricked.

4) I'm slightly afraid of getting bitten :/ My other corn snake was very used to being handled and very docile. I put a glove on when I held him for the first time (new snake, not my other corn), and he did strike at the glove. I want to get him used to being handled ASAP, because I love handling my snakes. Any tips on how to handle/tame an aggressive (more defensive really) snake?

Thanks for your input in advance!

1. Some of those under tank heat pads can hit 140 degrees or higher. I personally have plugged mine in and measured them with infrared thermometers. One of them hit 137 degrees and the other hit 124 degrees after being on for about an hour. I remember reading a post somewhere on this forum about somebody having one that hit 175 degrees.
There are some folks that will tell you a thermostat or regulator is not necessary with corn snakes. That the snake will find the spot he's comfortable in. Yet I can show you a picture of a corn snake that "Was Comfortable" coiled around a heat lamp where he was killed and promptly Cooked. Literally. If you want to see that picture I can show it to you. Common sense should tell you Any Source of Heat should be regulated in some way. I use thermostats on my pads. A thermostat can range in price anywhere from 10 bucks to a few hundred. You ought to be able to go out when the stores open this morning and take care of that problem. It doesn't have to be a big deal.

2. You need to secure the lid in some way. A corn snake will find its way out of the cage. It's not a matter of "if" but a matter of "when." Clips, ratchet straps, bungee cords, a different type of lid, all are possibilities, but yes, you need to do something.

3. I personally would not have a live cactus in a cage with a snake. I honestly don't know if it will hurt the snake or not, whether it's good or bad, but I just would not do it.

4. Anyone who owns a snake should expect to get bitten some day. A 12 foot long Boa can and will do some damage, a 2 foot Corn snake is not going to hurt you. The best way to make the snake more tame and less skittish, is to go ahead and show him you're not afraid of him and handle him anyway. He "should" eventually get used to you. I say "Should" because there are stories of corn snakes that years later still bite their owners. It's always a possibility you have a snake like that, but you won't know until you start regularly handling.

well done on taking him in