I have an inventory of 550 and that's my setup on Inventory Recycle tab:
80Pokeball
80GreatB
100Ultra
30Pot
80SuperPot
80HyperPot
30Revive
40Berry
The other space are used by MaxPot end other things, i'm taking in my inv so many potion 'cause when i get off work i'll hunt gym. (Always botting around where i work/live).
With a 300Inventory i think it is impossible to play. But if you are only lvling you can recycle everything and have only balls.
Last but not least, the catching setup
PokeBall 1
Grat 400
Ultra 750
It's working great at the moment, but i always bot near a lot of PokeStop so i always recycle items.