Some of the advice you’ve gotten so far has been conflicting. I would suggest picking one of those 3-drops to stay at 4-of, and then maybe consider adding others. (I would personally go with Rabblemaster because you don’t have much card draw, so you might run out of spells for Monastery Mentor). You can remove the Mardu Charms (I think they underperform) for space.
Roast is a pretty underwhelming card with Valorous Stance in the deck, so I would consider cutting them entirely. I know it’s attractive to have burn spells with Soulfire Grandmaster, but the Stokes and Strikes are going to be enough. Hordeling Outburst actually provides a lot of value for its cost, and works great with Stoke, Rabble, and Butcher. I would suggest moving the 1 you have into the maindeck and adding more to replace the Roasts you’re cutting. You’re very heavy on removal right now, so I would even consider switching Utter Ends into your sideboard in favor of another Planeswalker or two in the main.
Definitely draw some test hands, play a little on cockatrice, or ask someone you know to play a few games with you. It’s going to be hard to tune it without getting a feel for what you’re drawing when. This deck also might have trouble with decks that try to overwhelm you with many things -- Seismic Rupture (Arc Lightning, which you already have, might be better) or End Hostilities are good sideboard options to deal with those threats.
So ultimately, I suggest:
But in the end, it’s up to how you want the deck to play. If you really want to play a long control game, you probably want to give up the goblin synergies in favor of Mentor and draw spells (Outpost Siege, maybe even Tormenting Voice). There are also a lot of great resources on Channelfireball.com and Starcitygames.com, if you want a similar list to compare to, or to hear a pro’s take on the archetype. Happy brewing!
