New cage advice needed

I recently bought a 40 gallon breeder along with a heat mat for it. I was wondering what wattage I should use for the day light? Plus when changing cages should I give him time to adjust with no handling.
P.s. He is a ij/coastal mix. Just got him at the beginning of the month and has been in a 10 gallon.

No need for a day light at all. It's a snake so you don't need a UVB bulb. Also you have the heat mat so you don't need a heat bulb. That's what the mats for and they are better to use then bulbs as wellas they don't dry out the tank and you can maintain the heat better. Also make sure you have something on the mat to regulate the heat. A thermostat or rheostat/dimmer. Without these the heat mat WILL get too hot.

If you want the lamp just to ad some light to the tank then use the lowest wattage possible with a fluorescent bulb.

Yes when you change cage give him a week with no handling to adjust. It's no different then binging a new animal home. A 40g can sometimes be recommended as the right size for an adult carpet python on care sheets but they are actually a little bit small. If you just moved him from a 10g he is obviously still growing so the 40 works but a 4X2 foot tank is what you should use once the snake is full grown.

What are your ambient temperatures? An overhead heat source might be necessary, because a heat mat will only create the hot spot, and not do much for ambient temps. I prefer a ceramic heat emitter (CHE) over a light bulb, because you don't have to worry about the light cycle interfering with the snake's natural cycles (or turning off a light at night when it's usually coldest).

The ambient temperature is 76. Where do I find a themostat for the mat and how does it work with the heat mat?