The only real way to get them after completing the stretch goals is by leveling up, so 10 per level. So far I've only bought the "necessities", K.K.'s chair, Tom Nook's chair and the 2 extra crafting spots
I've only spent tickets on the extra crafting slots, the two chairs, and items storage space. Currently, I'm level 48, and with the tickets the game provides, I have my item storage space up to 200.
Having just started today, I bought KKs stool, then one extra item slot. I've rushed a couple things as well but I'm gonna try to collect for Tom nook although I never cared for him much...
I looked it up, and you get 900-something free leaf tickets from leveling up and completing goals and such. I spend my leaf tickets sparingly, so no nets, fertilizer, or honey for me. I'm also incredibly patient when it comes to games like this, so I just wait for a furniture item/amenity to be ready. The one thing I splurged on was the garden-style camper which cost 150 leaf tickets (it's the bigger camper type). I think it was a worthy investment, though. The one thing I will spend my leaf tickets on frequently is Shovelstrike Quarry, because you can get a good deal of cute essence from there sometimes.