I personally plan on keeping mine in a 4'x2'x15" as an adult cage, but have heard of plenty of people splitting that with a divider for 2 adults. An adult would be fine in a 3x2 but AP has the 4 footer cheaper than the 3 so might as well get the space. The key with a younger snake though is to make sure that if the cage is large that there's a lot of clutter (branches, hides, plants, etc) so they feel secure.
When I got my baby beep, I left her alone for the first couple weeks to let her settle, besides for feeding and maintenance. For the first few months I would handle her 2-3 times a week for about 5-10 minutes per session (no handling on feeding day or 48 hours after feeding).
Now I usually take her out twice a week for about 15 minutes, though once a month or so i'll bring her to my room and put her on my bed while I watch TV. She'll usually spend a couple minutes exploring the bed and will then curl up next to me and rest her head in my lap. She'll stay like that and chill and even fall asleep for an hour or so, when she starts moving again or looking to hide under blankets and pillows I know its time for her to go back in. However, I would not recommend handling sessions over 15-20 minutes until your snake is used to you, and you learn how to read its behavior and signs of stress