Here's how my first 3 years went, I'm easily at 99% completed.
Year 1 (thanks to others and multiple copies this was possible): All gold badges
Year 2 (narrowly missed this, the purple tulips were the final): Grow all flowers, trees, bushes, etc
Year 3 (this really required other players to accomplish): reach 100 dreamers, and 1,000 visitors
Year 4 (this is another one who needs others since I don't use Power Saves): 100% catalog
Year 5 (this will be tricky, but certainly possible): max out savings
That's as far as I see myself going, as Wild World got daily play for 5 years (or thereabout), so I anticipate putting 5 years into New Leaf which puts me in 2018, hopefully the next one will come out then, and I can easily "move on"- I still play WW on occasion, for that matter, I still play GameCube and City Folk semi-regularly too.
Just drag the stuff out, you can easily do all this on your own if you just focus on one thing at a time the entire year. It took me about 14 months to grow every single type of flower, but I did it on my own. I broke that into groups too, like grow all the cosmos, then roses, pansies, etc until I got them all. Purple tulips were the last due to how long some of the others took. When all you do everyday is water flowers, and talk to villagers it's a little easier. Just mix it up too, take time off, visit the island, do whatever, the game never truly ends, and even though I've nearly 100% WW, I still go back- maxing that savings was insane- INSANE!!