Thank you very much ^^! He'll certainly appreciate all that care and nurturing~
Right now we have five pieces of DLC planned; 3 Cove Expansion DLCs and 2 Love Interest DLCs. Cove DLCs unlock Moments on the main Moment Screen and Love Interest DLCs allow you to pursue someone other than Cove and unlock Moments on secondary screens that aren't in the demo. Cove DLCs will cost $3 USD, LI DLCs will cost $4 USD. So all together it'll be $17 USD + Tax (in most cases)!
Though, they won't come out all at once. On release day only some of the DLCs will be available and the rest will release over time. I hope that helps c: