First off - welcome to the Forum!
Now on to business - if the "guy" you were buying from did not suggest a thermometer for the Under the Tank Heater (UTH) then he may not have mentioned that it needs a thermostat to keep the temp at 90-91*F MAX. If it does not have one of these, turn it off IMMEDIATELY - it can and will burn your snake
The interior of the hot hide should be 88-90*F and the interior of the cool hide 80-83*F, the ambient air temperature should be 78-80*F, I like to aim for the warmer side of that. No temps anywhere in the cage should ever drop below 75 and never rise above 90-91*F
For hides, they need to be tight, dark, and secure - not those 1/2 log things. Your snake needs to be able to fit inside and comfortably curl up, its best if his sides are touching the sides of the hide
If he is in a tank, the top needs to be covered to maintain humidity of 55-70% (depending on shed schedule) or kept around 60 to be safe. Three sides of the tank need to be covered on the outside so he feels covered and safe. Fake plants can be added for cover.
All heat sources (cool hide, middle/ambient, and hot) need DIGITAL thermometers and the tank needs a DIGITAL hygrometer to measure both. The dial ones are not accurate. Also, nothing sticking should ever be in the tank.
Water bowl needs offered at all times.
Feed after a week of zero handling. Get a digital scale so you can weigh both him and his food. As a baby he needs to eat 10-15% of his body weight every 5-7 days. Don't worry about switching prey items yet - just make sure he eats. Once he has had 3 to 5 meals then you can start handling for short sessions. Just make sure not to handle withing 48-72 hours of feeding so he does not regurgitate
tttaylorr and Ax01 beat me to it - guess I'm too long winded lol