isabelle is pretty straightforward about what she wants you to do. if she says you need more flowers, raid the island and plant more flowers. if she says more trees, shake some fruit and plant a bunch. etc
keep in mind that in acnl (unlike some other AC games) you can't really over-plant your town. so just go nuts if she says she wants flowers or trees.
i believe you need eight (or maybe ten? you can't OVER-develop, so again, just make as many as you like) public works projects to hit perfect status.
however, if a villager moves away it counts as losing or demolishing a project and can knock you out of perfect status. this happened to a buddy of mine.
haha kaduk that's more a personal opinion than the town ranking, though.
i seem to recall wild world i had a constant fight going on with my town where i'd plant trees and it'd say i planted too many...so i'd chop a few down and it'd say there weren't enough. got really annoying!
what i meant more is that in this version, you can have as many as you like and having masses will not negatively impact your perfect town status.
This should help:
Perfect Town Requirements
The rating depends on three categories: Cleanliness, Abundant Nature and Abundant Living.
Cleanliness
less than 10 weeds
less than 10 items on the ground (not counting sea shells, fruit, mushrooms, flowers, buried fossils, buried gyroids, buried Pitfall Seeds)
no garbage (Empty Can, Boot, Old Tire, Spoiled Turnips)
no Rafflesia
Abundant Nature
Trees between 110 and 200
Flowers over 50
High Nature Points from Public Works Projects
Good: Flower Clock, Flower Bed, Flower Arch, Wisteria Pergola, Straw Fence, topiaries, Solar Panels, Wind Power Generator, Windmill
Bad: Garbage Can, Jumbo Monitor, Oil Excavator, Tire Play Equipment, Picnic Sheet, Traffic Light, illumination items, Tower
Abundant Living
High Living Points from Public Works Projects
Best: Campground
Good: bridges, benches, outside lights, Garden Chair, Hot Spring, Fire Hydrant, Stadium Lights, Solar Panels, Lighthouse
OK: almost everything else including Water Well, Fountain, clocks, Signboard, Face Board, signs, art, monuments, etc.
Bad: Garbage Can