My advice...scour the internet for all topics relating to kinky things and then write down all the ones you'd be interested in trying. Get him to go through checking "Yes" "No" or "maybe" against each act and you will have a great jumping off point. You can even ask him to rate them out of 10, based on how much he would like to try each act, then you will know which ones are at the top of his favourites list. Type "A to Z of Kink" or "lists of kinky activities etc, to find lots.
When you discover all of his favourites...broaden them. For example...he likes you spanking him with your hand. What about with a paddle? a flogger? What about standing up, or tied up, or made to kneel on the floor? Broaden, or flesh out each of the acts you most enjoy together this way.
Once you have a better idea what interests you both, you can start purchasing some toys and accessories to heighten the situation.
Submissives tend to all be very different and there isn't one kind of submission (or domination). Some submissives really get their kicks out of serving their Mistress/Goddess, while others crave pain pain pain. Some might get turned on through humiliation (sissification, name calling, asked to do embarrassing things), while others want to be nurtured...Honestly, there are lots of different twists and turns and the journey ahead is about getting into his head, working out his particular motives and what makes him tick.
Just take it slowly. No, it isnt easy to just suddenly be all dominant and vocal when you are completely new to this. So, start small. The "good boy" thing is a wonderful start. The next step might be to just be a little more demanding when you speak up. It doesnt have to be anything special, just "ON YOUR KNEES" or "BEND OVER" Gradually you could add more to this, like describing how silly he looks or how pathetic he is at pleasing you (if he is into humilation) or you could try a softer, more teasing approach, such as "oh babyyy, I bet you would love it if I wrapped my lips around you...such a shame you were a bad boy today" etc...
Just take it slowly basically. This includes the pegging idea. If he is new to anal, too much too soon could put him off due to pain or discomfort. The pleasure is in the journey. If you do get more into it, I really do recommend a safeword. This will allow him to be able to fight back and say "No please no" while at the same time, you will know that is just play. If he says RED, you know to actually stop. Being able to say no...while meaning yes, makes it feel more real for the submissive too. It can play into the fantasy.