Congratulations on getting your new P's! I'm sure it'll be a blast!
Now to answer your questions. You can get the Eco items from the Eco Triplets that you can see on the Tsubomi Park. They only appear during the 10th, 20th, and the 30th of the month and they only give you one item per visit.
For dating, your character must be on the adult stage. When you visit the Tsubomi Park, there is a chance of seeing a bachelor/bachelorrete. The first time you see them, they will just talk to you in the park. The second time you see them, they'll ask you on a date which you can accept or decline. The third time you see them, given that you accepted the date, they'll be asking for a marriage.
Alternately, you can go to the matchmaker for a faster marriage. It will be the 8th place on the door menu (
おみあいパーティ).
Hope this helps!