It should cover about 1/3 of the bottom of the tank. They have sizes rated for certain tank sizes.
Also, when you get identical hides, make sure they are the "rock cave" kind and not the half log kind. BPs prefer the more enclosed ones.
Make sure you also (if you haven't already) pick up at least one digital thermometer with a probe so you can measure the hot side temp and set it with your thermostat or rheostat.
As for the constant cruising, it is normal for a new snake. They are in a new environment and are just checking it out. Try to not handle him for a week. After a week is up you can offer him a meal. Then wait two days for him to digest and then you can start holding him on a regular basis. I know its hard. Trust me its like the longest week of your life but it is best for the snake![]()