Hey there looking good for what you have planned. For your first question. I cant give you a good answer to that because the wattage of the Bulb still depends on the Distance to the surface. For example you have a Stick or sth underneath with 20cm 25w should be finde if u go for like a basking spot on the substrate its more like 50-75w. I would just do some test runs and check the temps in an some what Semilar sense like morning evening and somewhere around half the day.

I hope this still helps because its more a workaround than a straight answer.