Can't really comment on your bulb because it's really more of a trial and error sort of thing because factors such as ambient temperature of the room, pressure, humidity, etc go into your cage temperature. 75w is a good start so when you set up your cage, take measurements and you can adjust your temps with different bulbs from there.
As for a full size cage, I personally don't have an issue. Some say that young animals might have trouble finding their food. I don't believe in this. Give them many pathways so they can cruise around the whole thing and they will find their food. It's instinctive to them to hunt for food. I made the jump to full size cage pretty early and I have no problem at all. Crickets would usually climb to the top anyways and gravitate toward the basking light. If you really feel that they will have trouble finding food, you can cup feed. Some chams take time to adjust to it but they will eventually eat out of the cup and you will know that your cham is getting their food. Or you can section off half the cage so your cham has less space to find their food.
Other then the food issue, there is no real cons about going with a big cage. Space is good for them.
