Awwww what a cutie! Lovely little one, congrats
On to your questions: If you got it on Friday, it'll still be pretty freaked by the change in environment, so leave it alone 3-4 days more without handling, or handling only for 5 mins each day if you can't leave it alone (I know how hard it is!). Then it'll be feeling more secure and not getting scared evertime this giant monster reaches in to try to catch and possibly eat it. Remember in the wild the babies would hang out somewhere safe away from predators until they got bigger.
After this settling in period, try feeding her a pinky. If all goes well (and it can take all night) then you're good to go on a 4/5 day feeding schedule. If it doesn't eat for you first time, don't be surprised! It's a bummer but their whole world did just change. Don't then try and feed every day, wait 4/5 days again until next attempt. It's not going to starve in that time. One of mine, same size as yours, went 3 1/2 weeks without eating, and now no feeding problems with it. After it's fed, don't handle it or bother it for 48 hours. Stressing them at this point can cause a regurge.
You don't need tongs to feed it. Put it in a different container, preferably smaller than it's viv (and escape proof!). If it came in a little deli cup with air holes punched in, that's perfect. Put the pinkie in the container first, quick hand wash, then in with the snake (so you don't smell of mouse). I put the deli cup back in the viv and lock it, turn off the lights and leave the room. Go back a couple hours later and hopefully you'll have a lumpy snake instead of a pinkie. Putting them in a small container with the food focuses their attention on it and ensure they don't eat any substrate. Also stops them from thinking that every time you open the viv a mouse is coming their way!
Try and end every handling session on a positive note. This means that if you open the viv to get the snake out, whatever it does, you still have to follow through. This is so it learns that posturing, striking, tail rattling will not stop you so it might as well not bother. If it does strike at you, try and ignore your natural instinct to pull back. Even if it does bite (most just sort of head-butt) it's not going to hurt. Your snake is cute and titchy, it'd be like getting savaged by a duckling. If it gets stressed out during the handling session or poops on you (this will happen eventually, have tissues at the ready!) keep on handling it until it calms down. Only put it back once it's nice and calm, and it'll eventually work out that calm=home/handling.
Did you get a thermometer? Very important to know the temps in the viv, and you need to know the bedding temp, not the air temp. Until you know how hot the UTH is making the bedding I'd probably leave it off all together. Snake will be fine for a few days at room temp.
Ok, I'll stop waffling now
Good luck with everything, keep asking those questions!
Edit: P.S. I really wish that shopkeepers generally know what they are talking about. Unfortunately...... not so much.
