This game is extremely fun.
You can beat the game without the premium plants for sure.. but in survival mode.. you can't get too far, because total damage per square is too low without doubling peas atk power
What's your typical strategy? I usually lay down a layer of sunflowers, and then use the mines and sacks to kill/slow down the zombies as I accumulate sun, then I start laying down peas where needed, while accumulating more and more sun, then I go ape**** and lay down all the plants and win. 
Use the leaf to accelerate the sunlight to get more pea shooters out early.
Or get cabbages and wait till there's a lot of zombies and use the leaf on them. Boom. 
For fast build.. I do this in PvZ (2)
Use imitater for 2x sunflower (single) each sunlight is 50.. use 1 leaf on 1 of the sunflowers.
This would allow you to spawn 4x flowers within the first 7-10 seconds. and keep doing this without using leaf.. until you have 2 rows of sunflowers before you put down any pea pods..