The first thing you should do is listen to some amps online and find the sound you want. No sense pointing you to a little 5 watter if you like cleans, a 40 watt might be a bit much if you like crunchy distortion. You say you like the Super Champ but can not crank it up. Since I do not know if you have this amp in your stable or just play through it and would like an amp similar for your own (it is about 20W) I will suggest two routes.
To add an amp to complement the SC I would say go to a Champ styled amp (if you find you like the sound), it will allow you to crank that little puppy up without having people ask you to turn it down (all things being relative).
To do a SC loudness kind of amp I would go the Princeton direction and find out who makes a board for this amp. I would not be too concerned with getting a kit as you say your dad has experience that you can rely on. Part of you two sourcing the parts yourself is for you to learn the method and reasoning in selecting the parts (I am assuming dad wants you to understand the process).
In between there is the 5E3 , can play louder than the Champ but gets dirtier before a Princeton. Throw in some negative feedback on a switch and it will clean up some. Could do a Brown Deluxe volume and tone control.
But the important thing is deciding on the sound you want.